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SESSION 3 REVIEW

RIVER FISHERIES: ECOLOGICAL BASIS FOR MANAGEMENT AND CONSERVATION

A.H. Arthington1,2 K. Lorenzen3 B.J. Pusey1,2 R. Abell4 A.S. Halls5 K.O. Winemiller6 D.A. Arrington7 E. Baran8

1 Co-operative Research Centre for Freshwater Ecology, Centre for Riverine Landscapes, Griffith University,

Nathan, Brisbane, Queensland 4111, Australia 2 Co-operative Research Centre for Tropical Rainforest Ecology and Management, Centre for Riverine Landscapes,

Griffith University, Nathan, Brisbane, Queensland 4111, Australia 3 Department of Environmental Science and Technology, Imperial College, London SW7 2BP, UK 4 WWF-United States, 1250 24th St. NW, Washington, DC 20037, UK 5 Renewable Resources Assessment Group, Department of Environmental Science and Technology, Imperial

College of Science, Technology and Medicine, Prince Consort Road, London SW7 2AZ, UK 6 Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX 77843-2258, USA 7 Department of Biological Sciences, University of Alabama, Tuscaloosa, AL 35487-0206, USA 8 WorldFish Center (formerly ICLARM), P.O. Box 500 GPO, Penang 10670, Malaysia

ABSTRACT

Large rivers and their floodplains sup-

port a significant proportion of the world’s

biodiversity and provide important goods and

ecological services to society, including fish-

eries. Riverine ecosystems and fisheries are

subject to intense pressure from a wide range

of anthropogenic disturbances, the main ones

being impacts from altered land use, modifi-

cations to river flow regimes, riparian and

physical habitat loss, water pollution, exotic

species invasions and intensive exploitation

of fish stocks. As a consequence, a far greater

proportion of freshwater species are threat-

22 Session 3 Review :

ened or endangered than terrestrial or marine species in

the same taxonomic groups. In this paper we review

ecological processes sustaining river and floodplain

biodiversity and productivity. We also outline the sta-

tus of knowledge of fundamental issues in fish ecolo-

gy, including fish habitat requirements, trophic ecolo-

gy, life history strategies, migration, the population

biology of riverine fish and modelling of fish popula-

tions and assemblages. We evaluate threats to the pro-

ductivity and diversity of large river systems, as well

as conservation and rehabilitation measures and dis-

cuss ecological approaches and tools for management

decision support. The final summary highlights knowl-

edge gaps and research priorities and new research

frontiers that demand more attention in river ecosys-

tem studies, conservation efforts and fisheries manage-

ment.

INTRODUCTION

Large rivers and floodplain ecosystems support

a significant proportion of the world’s aquatic biodi-

versity. Species richness within some tropical systems

surpasses that of marine ecosystems, including coral

reefs. The Mekong River, for example, contains 500

known fish species, with several hundred more species

lacking formal definition (Dudgeon 2000). The flood-

plains of large rivers are also amongst the most pro-

ductive landscapes on earth (Bayley 1988a;

Welcomme 2001). Fisheries in large rivers and their

associated wetlands and floodplains provide a major

source of food, employment and/or income that is cru-

cial to sustaining the livelihoods of multitudes of peo-

ple, particularly the rural poor in large areas of the

world. For example, fisheries are the single most

important source of income for floodplain dwellers in

the Amazon (Almeida, Lorenzen and McGrath 2002)

and match income from rice farming in rural house-

holds in Cambodia and Laos (Lorenzen et al. 2000).

H o w e v e r , due to their diffuse and inconspicuous

nature, inland fisheries are often grossly underreported

and undervalued.

Freshwater species are, on average worldwide,

more imperilled than their terrestrial and marine coun-

terparts (McAllister, Hamilton and Harvey 1997;

Stein, Kutner and Adams 2000). Of those species con-

sidered in the 2000 IUCN (The World Conservation

Union) Red List, approximately 30 percent of fishes

(mostly freshwater) are threatened (IUCN Species

Survival Commission 2000). At a regional scale, the

projected mean future extinction rate for North

American freshwater fauna is about five times greater

than that for terrestrial fauna and three times that for

coastal marine mammals. This rate is comparable to

the range of estimates predicted for tropical rainforest

communities (Ricciardi and Rasmussen 1999). Such

inventories can account only for described forms and

even within well-known groups such as fish, species

could be going extinct before they can be classified

(McAllister, Parker and McKee 1985).

Rarely is a given species imperilled as a result

of a single threat and it is often impossible to tease out

the intertwined effects of the many disturbances occur-

ring within a given watershed (Malmqvist and Rundle

2002). Only seven of forty recent extinctions of North

American fishes were judged to have a single cause

(Miller, Williams and Williams 1989). In a more recent

global analysis of fishes, Harrison and Stiassny (1999)

estimated that 71 percent of extinctions were related to

habitat alteration, 54 percent to exotic species, 26 per-

cent to pollution and the rest to hybridization, parasites

and diseases, or intentional eradication. On the Iberian

Peninsula, habitat alteration and water pollution were

identified as the most important causes of degradation

of native fish communities (Aparicio, Vargas, Olmo

and de Sostoa 2000), a pattern that may be typical of

developed countries. Exploitation, however, may be

more important as a threat to freshwater fish diversity

in some developing countries (Welcomme 1979;

1985). In analyses of threats, the categories themselves

often overlap, signalling the difficulty of isolating

proximate causes. As any conservation planner knows,

mitigating threats to freshwater biodiversity requires

understanding of a complex set of biophysical interac-

tions operating over a range of spatial and temporal

scales.

River fisheries : Ecological basis for management and conservation 23

Fisheries production and ecosystem conserva-

tion interests are often, but not necessarily, identical.

Certainly, intensive exploitation can be detrimental to

ecological integrity. A somewhat more insidious con-

flict arises when habitat modifications or species intro-

ductions impair ecological integrity but result in

increased fisheries production. For example, reservoirs

in the Sri Lanka dry zone retain significant amounts of

water in the upper basin for much longer than would

naturally be the case and support productive fisheries

based largely on introduced tilapias. Overall, this type

of modification of habitats and biota in small river

basins is likely to increase basin-wide fish production

(Lévêque1995; Lorenzen, Smith, Nguyen Khoa et al.

2002). However, impacts on native biodiversity and

ecological integrity, although rarely quantified, are

likely to be negative (World Commission on Dams

2000; Bunn and Arthington 2002; Naiman, Bunn,

Nilsson et al. 2002). As a result, conflicts may arise

between fisheries production and related livelihood

issues versus the maintenance or restoration of habitats

and river flow patterns that are critically important

from a conservation perspective.

Similar examples of divergence between fish-

eries and biodiversity conservation interests have been

reported from North American and European rivers

(Walters 1997; Arlinghaus, Mehner and Cowx 2002),

in particular where modified systems favour certain

species of particular fisheries or conservation interest.

Hence it is important to distinguish clearly between

fisheries production and conservation aspects of rivers

where the former are important, particularly in a devel-

oping country context.

To provide effective support for management,

river fisheries ecologists must analyse and predict

processes and impacts at the level of species, assem-

blages and ecosystem processes, in systems of high

spatial and temporal heterogeneity. This paper reviews

aspects of fish biology and ecology of importance to

biodiversity conservation and sustainable fisheries and

provides a perspective on the role of ecological knowl-

edge in river and fisheries management. We identify

key areas where ecological information is demanded

by managers and/or where scientists believe it should

be taken into account. The global water crisis and the

threat to riverine biota increase the necessity to deliver

models that serve science, management and policy. We

review the need to understand and predict river fish

population and assemblage dynamics, particularly in

relation to forecasting and mitigating the impacts of

human activities (such as flow regulation) and sustain-

ing fishery yields. Theoretical concepts describing

river ecosystems and ecological processes sustaining

biodiversity and productivity in large rivers must also

progress if we are to protect and restore damaged

ecosystems and sustain their fisheries production.

After reviewing recent developments, we dis-

cuss ecological approaches and tools for management

decision support, methods for integrating information

and novel approaches to resolving uncertainty. We

conclude with a summary of major points arising from

this review and the discussions held during LARS 2,

beginning with general statements to emphasize the

importance of rivers and fisheries and ending with a

perspective on conspicuous gaps in the science dis-

cussed at LARS. Throughout this summary we high-

light research priorities and new research frontiers that

demand more attention in river ecosystem studies, con-

servation efforts and fisheries management.

THE ECOLOGICAL BASIS OF RIVER FISHERIES AND

BIODIVERSITY

River hydrology and geomorphology

A fluvial hydrosystem comprises the whole

river corridor - the river channel, riparian zone, flood-

plain and alluvial aquifer. This hydrosystem can be

considered as four-dimensional, being influenced not

only by longitudinal processes, but also by lateral and

vertical fluxes and by strong temporal changes (Ward

1989; Arthington and Welcomme 1995). Rivers

and their floodplains are disturbance-dominated

ecosystems characterised by a high level of habitat het-

erogeneity and spatial-temporal fluxes of materials,

24 Session 3 Review :

energy and organisms are driven largely by fluvial

dynamics (Tockner and Standford 2002). Fluvial

hydrosystems provide corridors through the landscape

(Gregory, Swanson, McKee and Cummins 1991) and

the marginal zones (ecotones) provide buffers between

the watercourse and the variety of land uses within the

catchment (Cowx and Welcomme 1998).

A river basin can be characterised in a variety

of ways (Frissell, Liss, Warren and Hurley 1986). A

useful broad categorisation breaks the basin into three

longitudinal sections (upper/headwater, middle and

lower) and two lateral sections (upland and flood-

plain). Floodwaters and their silt load are dispersed lat-

erally within the middle and lower catchment, extend-

ing over the floodplain and carrying with them nutri-

ents, organic matter and organisms. The annual (or

more erratic) cycles of flooding and flow pulses ensure

the connectivity of river channels and their floodplains

and the silt, nutrients and organic load carried in the

floodwaters form and maintain the floodplain ecosys-

tems (Ward and Stanford 1995; Tockner and Stanford

2002).

The habitat components of the fluvial

hydrosystem include the main channel with its differ-

ent habitats: backwaters, side arms; floodplain lakes

and wetlands; estuaries and intermittent coastal

lagoons, man-made reservoirs and canals land subject

to seasonal flooding and non-floodable land that

nonetheless influences the quantity and quality of

r u n o f f received (Cowx and Welcomme 1998).

Temporal variation in discharge and habitat hetero-

geneity are closely linked and such linkages span a

wide range of time frames, from that of daily changes

associated with short-term floods or spates, to season-

al and decadal changes (e.g. creation of oxbows and

wetlands).

Hydrological variations associated with longer

time frames are also important. For example, drought

associated with El Nino events has been reported to

greatly influence riverine and estuarine fishes in

Suriname (Mol, Resida, Ramlal and Becker 2000).

Processes occurring over historical time spans may

continue to influence contemporary riverine ecology.

The Mary River of southeastern Queensland,

Australia, has cut down over 70 m into its bed in

response to sea level lowering during the Pleistocene.

Subsequent aggradation in the middle reaches has

raised the bed by 40 m but the river remains deeply

incised into the landscape (Bridges, Ross and

Thompson 1990). Such conformation has conse-

quences for the dissipation of flows during floods and

may influence in-stream production by limiting light

penetration. Long-term changes in discharge, channel

morphology and habitat and their interrelationship,

need to be carefully considered in light of projected

changes in global climate.

River ecosystems and processes sustaining

biodiversity and productivity

River ecologists have investigated various

functional linkages among riparian, floodplain and

river ecosystem components since the earliest studies

on large European rivers, but it is only relatively

recently that integrative frameworks have been pro-

posed for lotic ecosystems. The initial conceptual

frameworks were linear, particularly the River

Continuum Concept (Vannote et al. 1980), modified

for large rivers by Sedell, Ritchie and Swanson (1989),

the idea of nutrient “spiralling” (Elwood, Newbold,

O’Neill and van Winkle 1983) and the Serial

Discontinuity Concept (Ward and Stanford 1983).

Junk, Bayley and Sparks (1989) formalised the

“flood pulse concept” (FPC) at the first LARS meet-

ing, distinguishing lateral processes from concepts of

ecological continua along the length of rivers.

According to this model, flood conditions should be

associated with greater nutrient availability, aquatic

primary production (dominated by macrophytes),

allochthonous inputs and secondary production (espe-

River fisheries : Ecological basis for management and conservation 25

cially among juvenile fishes) in floodplain habitats.

The degree to which flooding occurs in phase with

warm temperatures and enhanced system productivity

influences selection for alternative life history strate-

gies of fish and other biota (Winemiller 2003). In

strongly seasonal floodplain systems, reproductive

cycles and associated migrations of fish have evolved

to exploit relatively predictable habitats and resources

on the floodplain (Welcomme 1985; Lowe-McConnell

1987; Junk et al. 1989; Winemiller and Rose 1992).

Physiological adaptation is also possible in response to

seasonal fluctuations in habitat condition and patterns

of distribution may be influenced by tolerance to natu-

rally fluctuating water quality (Hickley and Bailey

1987). In aseasonal flood-pulse regimes, fish are

“more challenged to respond appropriately to relative-

ly unpredictable patterns of resource variation”

( W inemiller 2003). One strategy shared by many

species in highly variable systems is to spawn and

recruit in main channels and backwaters under rela-

tively low flow conditions (Humphries, King and

Koehn 1999).

While the FPC has undoubtedly provided an

integrating paradigm for highly diverse and complex

ecological processes in river-floodplain-systems, new

perspectives have emerged from studies on floodplain

processes in different latitudes and continents (Junk

and Wantzen 2003). Walker, Sheldon and Puckridge

(1995); Dettmers, Wahl, Soluk and Gutreuter (2001)

and Ward, Tockner, Uehlinger and Malard (2001) sug-

gest that energy flow in large river systems might best

be viewed as an interaction of three concepts, the RCC

(downstream transport), the FPC (lateral transport to

and from floodplains) and the “riverine productivity

model” of Thorpe and Delong (1994), which describes

the role of autochthonous production. Some of the

major new developments in floodplain theory and

management include the importance of hydrological

connectivity (Ward, Tockner and Schiemer 1999;

Robinson, Tockner and Ward 2002; Winemiller 2003);

alternatives to the “highway analogy” with respect to

the ecological functions of the main river channel

(Galat and Zweimuller 2001); the ecological conse-

quences of erratic flow pulses (Puckridge, Sheldon,

Walker and Boulton 1998; Walker et al. 1995); and the

Multiple Use Concept developed for the central

Amazon River floodplain (Junk and Wantzen 2003).

A pervasive theme in river ecology and man-

agement is the importance of hydrological variability,

perceived by Walker et al. (1995) to operate at three

temporal scales: the flood pulse (days to weeks), flow

history (weeks to years) and the long-term statistical

pattern of flows, or flow regime (decades or longer).

Many ecologists perceive that the ecological integrity

and long-term evolutionary potential of rivers and their

floodplains depends upon the spatial and temporal

variability of the natural flow regime (e.g. Arthington

et al. 1992; Sparks 1992; Poff et al. 1997; Richter,

Baumgartner, Wigington and Braun 1997; Ward et al.

2001; Olden and Poff 2003). Poff et al. (1997) pro-

posed the “natural flows paradigm” as a blueprint for

management of river flows and river corridor restora-

tion and several methods for determining flow regimes

intended to protect or restore river ecosystems (i.e. by

providing environmental flows) are founded upon it

(Arthington and Pusey 2003; Arthington et al. 2003;

Brizga et al. 2002; Arthington and Pusey 2003; King,

Brown and Sabet 2003). Likewise, the UNESCO con-

ceptual tool “ecohydrology” (Zalewski 2003) suggests

that the sustainable development of water resources is

dependent on our ability to maintain established evolu-

tionary processes of water and nutrient circulation and

energy flow at the basin scale.

The ecological roles of littoral and riparian eco-

tones have received much attention in the recent liter-

ature on river-floodplain studies (Naiman and

Decamps 1997; Naiman et al. 2002). Riparian zone

processes influence river fish communities by way of

effects on individual fitness and species diversity,

mediated by changes in light and shade, water quality,

habitat quality and heterogeneity and trophic dynamics

26 Session 3 Review :

(Pusey and Arthington 2003). Sustaining the processes

linking riparian and river systems is crucial to the man-

agement, rehabilitation and conservation of river land-

scapes (Cummins 1992; Bunn, Pusey and Price 1993;

Wissmar and Beschta 1998; Naiman, Bilb and Bisson

2000).

Riverine fish assemblages: diversity, habitats and

trophic ecology

Biodiversity

Species richness in relation to area of habitat is

extremely high in many freshwater groups with an esti-

mated 10 000 fish, 5 000 amphibians and 6 000 mol-

lusc species dependant on freshwater habitats which

account for only 0.01 percent of the earth’s total aquat-

ic habitat. Other major groups dependent upon fresh-

waters include bacteria, fungi, plants, additional inver-

tebrate taxa, reptiles, birds and mammals. River con-

servation and management activities in most countries

suffer from an inadequate knowledge of the constituent

biota, especially in large, poorly investigated tropical

river systems (e.g. the Amazon, Saint-Paul 2003),

many Asian and southern African rivers (e.g. Dudgeon

2000; Shrestha 2003) and tropical Australian rivers

(Pusey 1998).

Rivers are islands of freshwater aquatic habitat

isolated from one another by terrestrial and marine

ecosystems. Studies of geographic variation in riverine

fish diversity have established significant relationships

between species richness and catchment area or dis-

charge (Welcomme 1985; Hugueny 1989; Oberdorff,

Guegan and Hugueny 1995; Oberdorff, Huegeny and

Guegan 1997; Guegan, Lek and Oberdorff 1998;

Pusey and Kennard 1996). In lowland rivers of the

southern llanos of Venezuela, interactions among sea-

sonal hydrology, variability in habitat structural com-

plexity and landscape heterogeneity appear to maintain

high aquatic species richness (Arrington and

Winemiller 2003). Likewise, multivariate models of

fish assemblage structure in Australian rivers demon-

strate the importance of catchment and local scale

habitat structure and hydrological variability (Pusey,

Arthington and Read 1995; Pusey, Arthington and

Read 1998; Pusey, Kennard and Arthington 2000).

Diversity of hydrological pattern appears to be central

to the maintenance of habitat heterogeneity and

species diversity (Ward et al. 2001; Tockner and

Stanford 2002).

Alteration of water quantity, seasonal flows

and patterns of flow variability (e.g. by damming and

abstraction, or inter-basin transfers - IBTs) have sub-

stantial and negative consequences for the mainte-

nance of biodiversity in many rivers (Arrington and

Winemiller 2003; Pusey et al. 2000; Bunn and

Arthington 2002). The disconnection of river channels

from their floodplains also affects biodiversity (Halls,

Hoggarth and Debnath 1998; Toth, Melvin, Arrington

and Chaimberlain 1998; Galat and Zweimuller 2001;

Robinson et al. 2002), with the magnitude of effect

likely to be greater in tropical and temperate seasonal

rivers than for temperate aseasonal rivers (Winemiller

2003). The further development of macro-ecological

models predicting regional variation in freshwater fish

diversity remains a task of major importance, given

that conservation plans to protect species from current

and impending threats (such as water use and global

environmental change) often seek to identify areas of

highest biological importance (Oberdorff et al. 1995).

Genetic analysis of the major populations of

fish species can reveal the geographic location, extent

and connectivity of genetically distinct stocks (Hogan

2003; So and Volckaert 2003) and thus inform fisheries

management and environmental impact assessments.

For example, dams and barriers to fish migration (Das

2003) may disconnect populations that now intermin-

gle and breed freely thus leading to depression of

genetic diversity (Jager, Chandler, Lepla and van

Winkle 2001; Matsubara, Sakai and Iwata 2001). IBTs

may connect distinct stocks with a long history of sep-

aration, undermining their genetic integrity and long-

term evolutionary potential (Davies, Thoms and

River fisheries : Ecological basis for management and conservation 27

Meador 1992; Bunn and Hughes 1997). Dams often

reduce the extent of downstream flooding and thereby

reduce the extent of connectivity between adjacent

river systems, with consequences for the genetic struc-

ture of regional fish populations.

Genetic studies can assist in the identification

of unique assemblages of species and genetic strains

and in the management of rare, endangered, “flagship”

or indicator species. Genetic analysis may also aid the

identification of processes threatening the genetic

integrity of metapopulations (e.g. unidirectional gene

flow) and mechanisms to minimise such impacts

(Jager et al. 2001; Matsubara et al. 2001). Resolution

of the systematics of many groups of fishes is needed

also to identify evolutionary significant units (ESUs)

and to identify at what scale conservation and fisheries

management strategies should be aimed (i.e. ESUs,

species or species complexes) (Mayden and Wood

1995). Neglect of such fundamental investigations will

inevitably result in management strategies lacking an

adequate biological foundation, with loss of biodiver-

sity and ecosystem services in the long term.

Distribution and habitat requirements

River networks have provided many opportuni-

ties for allopatric speciation of aquatic taxa and also

serve as reservoirs that accumulate species over evolu-

tionary time (Winemiller 2003). To assess the habitats,

populations and communities being managed and

opportunities for biodiversity conservation (Abell

2002), detailed surveys of the fish faunal composition

of individual river basins are needed, including major

tributary systems as well as main channels (Shrestha

2003). Ideally, such surveys should be undertaken

within a rigorous quantitative framework, in order to

provide meaningful and useful information on as many

aspects of organism biology as possible (density, micro

and macrohabitat use, population size structure) in

addition to distribution at the macrohabitat scale. This

type of information is proving immensely useful in

devising strategies to mitigate the impacts of flow

regime change in regulated rivers. Pusey (1998) and

Arthington, Rall, Kennard and Pusey (2003a) have

recommended fish data sets considered essential for

the determination of the flow requirements of river

fishes.

Specific habitat requirements of aquatic organ-

isms may be characterized by many factors, including

water depth, flow velocity, temperature and substrate.

Habitat preferences of different life stages of many

temperate fish species have been established and

expressed in the form of preference curves. Data on

habitat preferences are the crux of the earliest and most

widely applied methods to predict the ecological con-

sequences of flow regulation and water abstraction,

most notably the Instream Flow Incremental

Methodology (IFIM) and its physical habitat compo-

nent, PHABSIM (Bovee 1982; Stalnaker, Lamb,

Henriksen et al. 1994). As well as physical attributes,

water quality factors, in-stream and bank cover (Crook

and Robertson 1999; Pusey 1998; Pusey et al. 2000)

and biotic features/processes merit more investigation

to ensure suitable conditions of space, shelter and food

supplies for each life history stage (Power 1992; King

2002). For example, the distribution of some species

may be better predicted from knowledge of the factors

that determine the distribution of food items than it is

by habitat preferences defined by depth, flow and sub-

strate composition (Petty and Grossman 1996).

Habitat-centred methods for the assessment of mini-

mal and optimal stream flow requirements are dis-

cussed in more detail below.

Trophic ecology and food web structure

Sustaining river ecosystems and productive

fisheries depends upon understanding the energetic

basis of their productivity, linked to the trophic ecolo-

gy of fish and to food web structure. In many habitats,

algae seem to provide the most important source of pri-

mary production entering the grazer web (Lewis et al.

2001; Winemiller 2003), even in the highly turbid

28 Session 3 Review :

rivers of Australia’s arid-zone (Bunn, Davies and

Winning 2003). In contrast, fine suspended organic

matter apparently fuels the food web of the constrict-

ed-channel region of the Ohio River (Thorp, Delong,

Greenwood and Casper 1998). Even in species-rich

tropical rivers, most material transfer in food webs

involves relatively few species and short food chains

(3-4 levels, 2-3 links), i.e. remarkable “trophic com-

pression” (Lewis et al. 2001). Although longer food

chains that involve small or rare species are common

and increase ecological complexity, they probably

have minor effects on total primary and secondary pro-

duction (Winemiller 2003).

Seasonal rivers in nutrient-rich landscapes can

sustain greater harvest than aseasonal rivers or season-

al rivers in nutrient-poor landscapes (e.g. Carvalho de

Lima and Araujo-Lima 2003). However, the productiv-

ity of oligotrophic ecosystems can be enhanced by

“spatial food web subsidies” (Polis Anderson and Holt

1997; Winemiller 2003). For example, fishes that

migrate out of tributaries draining the floodplain dur-

ing the falling water period subsidize the food web of

the flowing channel by providing an abundant food

source for resident piscivores (Winemiller and Jepsen

2002). Food web subsidies can have major effects on

food web dynamics, even inducing trophic cascades

(Polis et al. 1997; Winemiller and Jepsen 1998; 2002)

and stabilising complex systems (Huxel and McCann

1998; Jefferies 2000).

The food web paradigm provides an approach

that allows us to model complex communities and

ecosystems with the ultimate aim of understanding

relationships and predicting dynamics (Woodward and

Hildrew 2002). To inform management, multispecies

fisheries in large rivers require a food web perspective

because stock dynamics are influenced by both bot-

tom-up factors related to ecosystem productivity and

by top-down factors influenced by relative densities of

predator and prey populations (Winemiller 2003).

Water resource infrastructure can modify aquatic food

webs by regulating downstream transport of organic

carbon, modifying water transparency and changing

the extent of movement of fishes throughout the river-

ine landscape (Jordan and Arrington 2001), such

changes impacting river fisheries (Barbarino Duque,

Taphorn and Winemiller 1998). Empirical models

relating fish diversity to discharge (e.g. Guegan et al.

1998) suggest that reductions in discharge will neces-

sarily result in reductions in diversity and this effect is,

at least in part, likely to be due to changes in food web

complexity (Livingston 1997).

POPULATION BIOLOGY OF RIVERINE FISH

Life histories

Most fish (and other exploited aquatic organ-

isms such as crustaceans and molluscs) have complex

life cycles involving several morphologically distinct,

free-living stages such as eggs, larvae, juveniles and

adults. In the course of their lives, many organisms

will grow by several orders of magnitude in mass and

their resource and other ecological requirements may

change drastically. As a consequence, many aquatic

o rganisms undergo ontogenetic shifts in habitat

requirements. Even so, habitat requirements and even

life cycles are not necessarily set in stone. Some

species, such as tilapias (Arthington and Bluhdorn

1994; Lorenzen 2000), display considerable plasticity

in their life histories and can cope well (or even bene-

fit from) changes in habitat availability. Others show

very little plasticity and may become locally extinct as

a result of even small environmental changes. For

example, the introduction of novel predators caused

the local extinction of the Lake Eacham rainbowfish,

Melanotaenia eachamensis, in Australia (Barlow,

Hogan and Rogers 1987).

Life history characteristics of fish, including

maximum size, growth rate, size at maturity, fecundity

and migratory behaviour, have important implications

for populations as well as their risk of extinction

(Winemiller and Rose 1992; Parent and Schriml 1995;

Denney, Jennings and Reynolds 2002). While life his-

River fisheries : Ecological basis for management and conservation 29

tory theory has been increasingly used to assess

exploitation threats to marine fish stocks arising from

fishing pressure, there has been far less work on fresh-

water populations that face a far wider set of threats.

In the following sections we review key aspects

of fish life histories and population ecology.

Habitat use and migrations

To meet the different requirements of different

life history stages, most aquatic organisms require

access to a variety of habitats in the course of their life

cycle. This requirement has two implications: (1) a

variety of habitats must exist and (2) organisms must

be able to migrate between them (actively or passive-

ly). Migration requires some degree of connectivity

between aquatic habitats, which can be highly frag-

mented and separated spatially.

Migration has evolved as an adaptive response

to natural environmental variation on a daily, seasonal

and multi-annual basis, with biomes and habitats visit-

ed during the life cycle and distance travelled being

essential characteristics of fish migration. Migrants

must respond to the right cues, travel at the right pace

and arrive at their destination within a certain time

interval. Embryos, larvae and juveniles must find

appropriate shelter and feeding grounds in order to

reach the size threshold at which they maximize their

survivorship. Migration also acts as a mechanism of

e n e r gy transfer (“subsidy”) between biomes and

ecosystems (Winemiller 2003) as discussed above.

Gross, Coleman and McDowall (1988) suggest that

various forms of diadromy (i.e. catadromy, anadromy)

have evolved in response to differences in marine and

freshwater productivity and it seems likely that the

evolution of potamodromy may also reflect spatial dif-

ferences in aquatic production within river networks.

Many fisheries in large rivers are based mainly

on migratory species. For example, medium to large-

sized characiforms with wide distribution on the flood-

plains of the Amazon/Solimões and other rivers

migrate by descending the nutrient-poor, clear and

black-water rivers to spawn in the nutrient-rich, white-

water rivers that originate in the Andean ridge. The

high abundance attained by these species may be a

consequence of their tactic of migrating towards nutri-

ent-rich habitats to spawn and using floodplain habi-

tats as nursery grounds (Carvalho de Lima and Araujo-

Lima 2003). The study of fish migrations has emerged

as a key area of fisheries research in the Mekong River

Basin (Warren, Chapman and Singhanouvong 1998;

Baird, Flaherty and Phylavanh 2000). Preliminary evi-

dence suggests that changes in fishing activities in

Cambodia may have resulted in changes in fish catch-

es in southern Laos (Baird and Flaherty 2003), high-

lighting the need for fish management strategies that

transcend national jurisdictions.

Similarly, in rivers where diadromous fishes

are an important component of the overall riverine

fishery, management strategies (and river fisheries val-

uation studies) need to transcend the distinction

between freshwater, estuarine and marine habitats and

to more properly consider critical chains of habitats.

Over-exploitation of piscivorous migratory species in

marine or estuarine systems may potentially affect far-

removed populations of fishes in freshwaters by alter-

ing top-down processes of regulation (Winemiller and

Jepsen 2002). Fully integrated (freshwater/estuary

/coastal) biological monitoring programs would

address these dependencies but appear to be lacking in

most large river systems, even though the close rela-

tionship between discharge and coastal fish production

has been documented in both temperate and tropical

rivers (e.g. Loneragan and Bunn 1999 and references

therein).

Determination and regulation of abundance

Management for both exploitative and conser-

vation purposes requires an understanding of the

dynamics of populations as a whole. Losses, through

emigration and death and gains, through immigration

30 Session 3 Review :

and birth, are integral to an understanding of popula-

tion dynamics and have received much attention in the

ecological literature (Humphries et al. 1999).

The abundance of fish populations is deter-

mined by a combination of density-dependent and den-

sity-independent factors. Compensatory density

dependence regulates the abundance of populations

and its magnitude has important implications for the

population dynamics of exploitation and disturbances

(Rose et al. 2001). The sustainable exploitation of pop-

ulations is possible only because populations compen-

sate for the removal of animals by density-dependent

improvements in natural mortality, growth and repro-

ductive rates. Likewise, populations can compensate

for the loss of individuals as a result of pollution and

other environmental catastrophes. Density-dependence

has been detected in mortality, growth and reproduc-

tive traits of fish populations (Bayley 1988b; Rose et

al. 2001). While traditional age-structured models of

fish population dynamics assume that regulation

occurs predominantly through density-dependent mor-

tality at the juvenile stage, recent studies have pointed

to the importance of density-dependent growth and

reproductive parameters in the recruited population

(Post, Parkinson and Johnston 1999; Lorenzen and

Enberg 2002). Regulation in the late juvenile and adult

population implies a greater potential to compensation

for increased mortality rates in juveniles (e.g. as a

result of juvenile habitat loss, or losses due to entrain-

ment), but also lower potential benefits of increasing

juvenile survival or abundance (e.g. by stocking of

hatchery fish) as compared to populations regulated

only at the juvenile stage. A good quantitative under-

standing of regulatory mechanisms is therefore impor-

tant to management and conservation decisions, but

our knowledge base in this respect remains relatively

poor.

The relative importance of density-dependent

and density-independent processes in determining

population abundance is difficult to assess and model.

This is particularly so in river systems characterized by

extreme environmental variability, where disturbance

can be a major factor (Reeves et al. 1995). Recovery

from disturbance is typically rapid in temperate fish

populations, although rates of recovery vary according

to the types of disturbance (i.e. pulse or press)

(Detenbeck, DeVore, Niemi and Lima 1992;

Winemiller 1989b; 1996; Winemiller and Rose 1992).

Population processes

Reproduction and recruitment

Various recruitment models or hypotheses have

been put forward, attempting to explain how fish in

early life history stages encounter sufficient quantities

of food of the right size, while avoiding predation. One

of the pre-eminent hypotheses is the “match/mis-

match” hypothesis of Cushing (1990), which recog-

nizes that fish spawn at approximately the same time

each year, but that prey abundance is less predictable

and more responsive to the vagaries of oceanic condi-

tions. Thus, in years when larvae and prey coincide or

‘match’, there will be strong recruitment, whereas in

years when larvae and prey do not coincide (‘mis-

match’), there will be poor recruitment. Under experi-

mental conditions in dry season waterbodies in

Bangladesh, Halls et al. (2000) found the recruitment

of a typical floodplain fish to be strongly dependent

upon both spawning stock biomass (egg density) and

biolimiting nutrient concentrations. These responses

were believed to reflect cannibalism by adult fish on

larvae and juveniles, competition for shelter from

predators and the abundance of food organisms for

developing larvae.

Harris and Gehrke (1994) proposed a ‘flood

recruitment model’ similar to the flood pulse concept

(Junk et al. 1989), to explain how some species of fish

in the Murray-Darling Basin, Australia, respond to

rises in flow and flooding. Humphries et al. (1999)

questioned the generality of this model, based mainly

on the fact that flooding in large areas of the Murray-

Darling Basin does not coincide with peak spawning

River fisheries : Ecological basis for management and conservation 31

times for many species and there are no published

accounts of larvae being found on the floodplain.

Whilst not dismissing the potential importance of the

floodplain, Humphries et al. (1999) proposed the ‘low

flow recruitment hypothesis’, which describes how

some fish species spawn in the main channel and back-

waters during periods of low flow and rising water

temperatures. Ironically, only the introduced carp

(Cyprinus carpio) seemed to respond to flood events in

the Murray-Darling system with a renewed bout of

spawning. More recently, King (2002) proposed five

reproductive strategies among fishes of Australian

floodplain rivers (generalists, flood opportunists, low

flow specialists, main channel specialists and flood-

plain specialists).

Establishment and defence of territories, feed-

ing, cues for reproduction and rearing of young are all

critical for the production of the next generation. Yet

our ignorance of these processes and how they are

affected by environmental disturbances caused by the

actions of humans is profound.

Mortality

Numerous and often interacting factors affect

natural mortality rates in fish (including predation, dis-

ease, starvation, abiotic factors, spawning stress and

senescence), yet our understanding of the importance

of different sources of mortality remains poor, particu-

larly for riverine fish. Mortality is strongly dependent

on body size in fish (Lorenzen 1996). It is greatest in

early life history stages, where variation in mortality

rates plays a major role in determining the strength of

cohorts. Whereas predation and starvation are assumed

to be the primary reasons for high mortality, informa-

tion on the links between these processes and alteration

to the natural environment is virtually non-existent.

Overall mortality rates decline as juveniles grow, but

mortality at the juvenile stage is generally believed to

be most strongly density-dependent. Moreover, juve-

niles may also disperse considerable distances and thus

are vulnerable to artificial barriers and other anthro-

pogenic as well as natural threats (Gallagher 1999).

The juvenile stage in fishes is often the most

difficult to study and hence knowledge of this stage

(including mortality rates and the factors influencing

them) remain particularly poor. In seasonal river-

floodplain systems, extremely high density-dependent

and density-independent mortality rates may be associ-

ated with the period of receding water levels, when

fish may become stranded and densities in remnant

water bodies can increase by several orders of magni-

tude relative to flood conditions (Welcomme 1985;

Halls 1998). This seasonal mortality pattern has major

fisheries management implications. Intensive harvest-

ing during receding floods may replace rather than add

to the high natural mortality at this stage and conse-

quently, floodplain fisheries may be able to sustain

very high levels of exploitation during the recession

phase. Conversely, however, these fisheries may be

very vulnerable to exploitation of the remnant dry sea-

son stocks that form the basis for future recruitment.

Growth

Body growth is an important population

process in fish, because it has a major impact on pop-

ulation biomass development as well as reproduction.

Growth in river and floodplain fish is strongly influ-

enced by environmental conditions, including hydrol-

ogy (Bayley 1988a and b; De Graf et al. 2001), food

resources and population density (Halls 1998; Jenkins

et al. 1999). In at least one highly channelized river

(Kissimmee River, Florida, USA), the restoration of a

more natural hydrologic regime has resulted in

increased growth rate and maximum size of a target

game fish, M i c r o p t e r us salmoides (Arrington and

Jepsen 2001).

Population dynamics

There are two aspects that set the dynamics of

river-floodplain fish populations apart from those of

fish populations in other habitats: the strong influence

of hydrological variation and the dendritic structure of

riverine metapopulations (Dunham and Rieman 1999).

32

The influence of hydrology on population

dynamics is most striking in seasonal floodplain sys-

tems where aquatic habitat may expand and contract

by over three orders of magnitude and populations may

respond with extreme cycles of production and mortal-

ity (Welcomme and Hagborg 1977; Halls, Kirkwood

and Payne 2001; Halls and Welcomme 2003). As a

direct consequence of this response, floodplain fish

stocks can withstand very high levels of harvesting

during the period of receding waters. Indeed, simula-

tion studies described by Welcomme and Hagborg

(1977) and Halls et al. (2001) both indicate that yields

from floodplain fisheries can be maximized by remov-

ing a significant proportion (up to 85 percent) of the

population just prior to the draw-down period. Perhaps

not surprisingly, this corresponds to the period of max-

imum fishing activity in most floodplain fisheries (de

Graaf et al. 2001).

Overall, quantitative modelling of population

dynamics in relation to habitat factors, such as hydro-

logical variables and land use change, is a relatively

recent development (Welcomme and Hagborg 1977;

Peterson and Kwak 1989; van Winkle et al. 1998;

Jager, van Winkle, Holcomb 1999; Gouraud et al.

2001; Halls et al. 2001; Lorenzen, de Graf and Halls

2003a; Halls and Welcomme 2003; Minte-Vera 2003).

Whilst validation of the models is required, good fits

have been achieved using long time-series data sets

from Bangladesh. Individual-based simulation models

provide a powerful means of exploring any effects of

different hydrological conditions on the dynamics and

production of riverine fish, providing valuable insights

to improve water use management at local and basin-

wide scales. More work is required, in particular with

respect to systems where large-scale hydrological

modifications are likely in the future and/or restoration

of natural hydrological regimes is but a distant possi-

bility (i.e. in many areas of the developing world).

However, even in pristine or restored river systems,

climate change is likely to lead to significant hydrolog-

ical change within the next few decades and under-

Session 3 Review :

standing population responses to such changes will

become increasingly central to fisheries management

and conservation.

Most river fish populations have a metapopula-

tion structure, i.e. they are comprised of local-scale

sub-populations that are subject to relatively frequent

extinction and re-colonization (Schmutz and Jungwirth

1999; Matsubara, Sakai and Iwata 2001). Gotelli and

Taylor (1999) show that conventional metapopulation

models that do not account for gradients may poorly

describe the behaviour of riverine metapopulations.

Connectivity patterns in river systems differ from

those found in terrestrial habitats. The dendritic struc-

ture of the river habitat implies that fragmentation of

rivers results in smaller and more variable fragment

sizes than in two-dimensional landscapes and a possi-

ble mismatch on the geometries of dispersal and distur-

bance (Fagan 2002). As a result, fragmentation of

riverine habitats can have more severe consequences

for population persistence than would be predicted

from models for two-dimensional landscapes.

ANTHROPOGENIC IMPACTS ON RIVER ECOLOGY AND

FISHERIES

Many types of river ecosystem have been lost

and populations of many riverine species have become

highly fragmented due to human intervention

(Dynesius and Nilsson 1994; Bunn and Arthington

2002). Over three quarters of the 139 major river sys-

tems in North America, Mexico, Europe and Republics

of the former Soviet Union are affected by dams, reser-

voir operation for different purposes, interbasin diver-

sions and irrigation (Dynesius and Nilsson 1994). The

range of human activities known to damage and

degrade river systems includes: (1) supra-catchment

effects such as inter-basin transfers of water, acid dep-

osition, climate change, (2) catchment land-use

change, (3) river corridor ‘engineering’ and (4) in-

stream impacts (Boon, Calow and Petts 1992;

Arthington and Welcomme 1995; Junk 2002).

Increasingly, aquatic ecosystems are being impacted

River fisheries : Ecological basis for management and conservation 33

by recreation and tourism (Mosisch and Arthington

1998). The following sections briefly review anthro-

pogenic impacts on river ecosystems and fisheries and

measures for the mitigation of impacts.

Supra-catchment effects

Supra-catchment effects such as acid deposi-

tion, inter-basin transfers and climate change increas-

ingly affect river ecosystems and fisheries in multiple

catchments and bioregions simultaneously.

Acidification of surface waters has caused a suite of

new pollution problems in industrialized areas, with

massive impacts on aquatic habitats and fisheries

(Brocksen and Wisniewski 1988). The general effects

of toxic pollution and acidification are first, the elimi-

nation of the most sensitive aquatic species and, as the

loading increases, the production of large tracts of

river that do not support fish. Climate change affects

temperature, but most importantly the spatial and tem-

poral distribution of rainfall and consequently river

hydrology and ultimately geomorphology, habitat and

biotic processes. Climatic or man-made changes to the

environment may compromise finely adapted fish

reproductive and migratory strategies, to an extent

largely depending on the intensity and recurrence of

the perturbation and on the adaptability of the species.

Catchment land-use and river corridor engineering

Changes in catchment land-use affecting rivers

include afforestation and deforestation, urbanisation,

agricultural development, land drainage and flood pro-

tection. Corridor engineering includes flow and flood

transformation by dams, weirs and levees, channeliza-

tion and dredging, water abstraction and the removal

or deterioration of riparian vegetation.

In many river systems land use change and cor-

ridor engineering are the most important factors affect-

ing fish ecology and fisheries. These impacts arise pri-

marily from changes in habitat availability (both quan-

tity and quality) and habitat connectivity (Trexler

1995; Toth et al. 1995; Toth, et al.1998; Bunn and

Arthington 2002; FAO 2000). Loss of habitat connec-

tivity has resulted in the local extinction of many

migratory species including shads, salmonids and stur-

geons (Boisneau and Mennesson-Boisneau 2003;

Faisal 2003; Fashchevsky 2003; Gopal 2003) and the

diminished abundance of floodplain migrant species

(Halls et al. 1998). Many rivers still face the threat of

loss of connectivity and its ecological consequences.

For example, the largest dam in the world, the Three

Gorges Dam in the Yangtze River basin of China, will

create a reservoir 600 km in length, reaching from

Sangliping to Chongqing. Closure of this dam will

cause blockage of fish migrations, extensive loss of

riverine habitat and profound ecological changes that

will threaten fish biodiversity in the river (Fu Cuizhang

et al. 2003).

The impacts of hydrological change (e.g. by

damming of rivers) may affect individual fish in any

history stage, biotic assemblage structure and ecosys-

tem processes. These impacts have been observed at

multiple spatial and temporal scales (Wo r l d

Commission on Dams 2000; Bunn and Arthington

2002). Only a brief review of key issues can be provid-

ed here. Pulsed reservoir discharges associated with

on-demand hydroelectric power generation limit the

quality and quantity of habitat available (Valentin et al.

1994), causing fish to become stranded on gravel bars

or trapped in off-channel habitats during rapid decreas-

es in flow. The timing of rising flows serves as a cue to

the spawning of certain fish species and loss of these

cues may inhibit reproduction (King, Cambray and

Dean Impson 1998), whereas cold-water releases from

dams have been found to delay spawning by up to 30

days in some fish species (Zhong and Power 1996) or

even inhibit spawning entirely. Larval development

can be inhibited by cold-water releases. Furthermore,

anoxic waters are often released from reservoirs in

which the vegetation has not been removed prior to

filling (e.g. Petit Saut Dam, Sinnamary River, French

Guyana), causing mortality in many river species.

Changes in river hydrology that are not in natural har-

34

mony with seasonal cycles of temperature and day-

length may influence many critical life history events

and have negative impacts on fish and other biota

(Bunn and Arthington 2002). Natural flood regimes

(and other aspects of the natural flow regime) are crit-

ical for maintaining biodiversity and fisheries, espe-

cially in strongly seasonal systems (Welcomme 1985;

J u n k et al. 1989; Agostinho and Gomes 2003;

Winemiller 2003), but also in rivers with less pre-

dictable flooding regimes (Puckridge et al. 1998;

Pusey et al. 2000). Ecological restoration of hydrolog-

ically degraded river floodplain systems should pay

careful attention to restoration of the historical hydro-

logic regime including natural periods of low and high

flow and periodic extreme flood and drought events

(Toth et al. 1997).

In-stream impacts

Exploitation

Many fisheries, particularly in the tropics,

exploit a wide range of species. In such multi-species

fisheries, the relationship between total effort and

long-term total yield (obtained from a range of differ-

ent species) tends to be asymptotic, i.e. yield increases

initially with effort but approaches a constant maxi-

mum over a wide range of higher effort levels

(Welcomme 1985, 1999; Lae 1997). This is because, as

exploitation increases, large and slow-growing species

are depleted and replaced by smaller, fast-growing

species that can produce high yields even at very high

levels of exploitation. Even though multi-species

yields can be maintained at very high levels of fishing

effort, it is neither economically nor ecologically desir-

able to operate at very high effort. Economically, the

returns to individual fishers tend to diminish with

increasing effort (albeit not linearly) and at the level of

the overall fishery, unnecessarily high levels of

resources are expended to achieve the same fish catch

that would be achieved at much lower effort levels.

However, where access is open and opportunity costs

are low, fisheries tend to be over-exploited in this way.

The small fast-growing species that dominate catches

Session 3 Review :

at high effort levels are usually less valuable in mone-

tary terms than the large species they have replaced,

but the nutritional value of small fish eaten whole is

extremely high (Larsen et al. 2000; Roos et al. 2002).

Ecologically the overexploitation of larger species -

“fishing down” the food web (Pauly et al. 1998) is

obviously undesirable because it may threaten the very

existence of some of these species. Of course, even

multi-species yield must decline at very high levels of

fishing effort (when even the most productive species

are overexploited), but whether this point has been

reached in many fisheries is questionable.

Recreational fisheries tend to have less drastic

impacts than food fisheries in that the target species are

generally limited and when these species are over-

exploited there are rarely shifts to smaller elements of

the community. It is also likely that loss of much genet-

ic variability occurs before a species is eliminated from

the fishery or the community. Total disappearance of

species through this process is comparatively rare,

although in some cases such as the Oueme River in

Benin, Africa, species (e.g. Nile perch, Lates niloticus)

have become commercially and ecologically extinct at

the local scale (Welcomme 1999). Where biological

extinctions follow, this is usually the result of com-

bined environmental and fishing pressures.

Introduced species

With progressive deterioration of native fish

stocks as a result of over-exploitation and other envi-

ronmental impacts, many countries have turned to

exotic species as substitutes, rather than addressing the

underlying causes of fisheries degradation (Welcomme

1988). In many instances fish have been introduced to

satisfy local anglers with strong preferences for exotic

angling species of international repute (e.g. salmonids

and bass). Fish have also been introduced deliberately

for pest and disease control (especially the mosquito

fishes), as ornamental species for aquariums, parks and

botanic gardens (Lobon-Cervia, Elvira and Rincon

1989; Arthington 1991) and as a source of protein for

River fisheries : Ecological basis for management and conservation 35

human populations (e.g. tilapias, carps). Fish intro-

duced for fish-farming have also escaped and

colonised local waterbodies and even most of some

large drainage basins (e.g. carp in the Murray-Darling

Basin, Australia).

The major modes of impact associated with

introduced fishes (both exotic and translocated) are

genetic effects via hybridisation, alterations of habitat

and water quality, consequences to native populations

of competition for space and food and from predation

and impaired health from imported parasites and dis-

eases (Moyle and Light 1986; Arthington 1991; Pusey

et al. 2003). Environmental impacts due to introduced

fishes frequently exacerbate the effects of over-fishing,

river regulation, habitat destruction and water pollu-

tion and these disturbances themselves often provide

ideal conditions for introduced species (Arthington,

Hamlet and Bluhdorn 1990; Bunn and Arthington

2002). However, despite decades of empirical studies

and some experimental work, our capacity to predict

the species most likely to become established, spread

and impact of introduced species is still very limited

(Moyle and Light 1996; Williamson and Fitter 1996).

Many countries have used risk assessments to identify

potentially invasive species (see Arthington et al.

1999; Leung et al. 2002) and then placed restrictions

on the range of species imported from other continents.

The translocation of native fish species that are not

endemic to particular basins should also be restricted

(Pusey et al. 2003).

Fisheries enhancement and supplementation

Aquaculture-based fisheries enhancement and

supplementation programs are frequently used in river

and floodplain systems. Such programmes may serve a

variety of purposes, from supplementation of indige-

nous populations for conservation to culture-based

fisheries of exotic species exclusively for fisheries pro-

duction (Cowx 1994; Welcomme and Bartley 1998).

Particularly common are programmes to maintain pop-

ulations of large migratory species threatened by loss

of habitat connectivity (e.g. salmonids, sturg e o n s ,

major carps) and/or to enhance fisheries production in

storage reservoirs and floodplain habitats. There are

good examples where the stocking of hatchery fish has

contributed to the conservation or restoration of popu-

lations (Philippart 1995), or led to substantial increas-

es in fisheries production with little environmental cost

(Lorenzen et al. 1998). However, many aquaculture-

based enhancements have proved ineffective and/or

ecologically and genetically problematic (Meffe 1992;

Lorenzen in press). Compensatory density-dependent

mechanisms imply that stocking into naturally repro-

ducing populations tends to reduce vital rates (growth,

survival, reproduction) of wild fish unless their densi-

ty is far below the environmental carrying capacity.

Stocking of hatchery fish may also increase the trans-

mission of infectious diseases or introduce new dis-

eases into wild stocks. Genetic risks to natural popula-

tions arise from low effective population size of hatch-

ery-reared fish (leading to inbreeding depression) and

from loss of local genetic distinctiveness and adapta-

tion if hatchery fish are not derived from local popula-

tions (leading to outbreeding depression). Where exot-

ic species are used for enhancement, this may give rise

to strong and sometimes unexpected ecological inter-

actions with native species, as well as to hybridization

between the exotic and related native species

(Arthington and Bluhdorn 1996). However, there is lit-

tle evidence for the common assumption that ecologi-

cal and genetic risks of stocking native species are nec-

essarily lower than those of stocking exotics (see also

Pusey et al. 2003). Potential and actual benefits and

risks of any stocking programme should be assessed

carefully and there are now several frameworks to

assist in this task (Cowx 1994; Lorenzen and Garaway

1988).

Aquaculture

Aquaculture is the farming of aquatic organ-

isms, usually confined in facilities such as ponds or

cages. Where cultured organisms escape into natural

systems in significant numbers, this may raise ecolog-

36

ical and genetic concerns similar to those encountered

in fisheries enhancement and supplementation

(Arthington and Bluhdorn 1996). Most aquaculture

systems rely on external inputs of feeds and/or fertiliz-

ers and large-scale aquaculture can be a significant

source of nutrient pollution (Baird et al. 1996).

C O N S E R VAT I O N , M I T I G AT I O N A N D R E H A B I L I T AT I O N

P R I O R I T I E S

The global assessments of the World Resources

Institute (Revenga et al. 2000), the IUCN (Darwall and

Vié 2003) and others (Miller et al. 1989) all indicate

the serious vulnerability and degradation of inland

water habitats world-wide. To address these issues,

three levels of intervention - preservation/protection,

mitigation and rehabilitation/restoration - are appropri-

ate for the protection of lotic systems, depending upon

the degree and type of modification and the level of

investment society chooses to make. Here we review

methods, opportunities and progress with river conser-

vation, mitigation and rehabilitation.

Identifying conservation areas

There is widespread agreement that it is far

cheaper for society to prevent degradation of rivers and

their floodplains in the first place than it is to restore

degraded aquatic ecosystems. The first challenge for

managers and policy makers is therefore to review the

legislative and institutional background to biodiversity

conservation and river protection and then to identify

and protect relatively undisturbed large rivers and river

basins that are representative of the world’s lotic biodi-

versity (Arthington et al. 2003a). Apart from their her-

itage values, conserved rivers and wetlands will serve

in the future as the major sources of propagules and

colonists for degraded rivers and wetlands that have

already lost much of their biological diversity (Frissell

1997; Arthington and Pusey 2003). Clearly a method is

needed for prioritising inland water sites for conserva-

tion at both local and regional scales.

Several major conservation org a n i s a t i o n s ,

including WWF and The Nature Conservancy, identify

Session 3 Review :

priority areas and strategies through ecoregion plan-

ning (Groves et al. 2002; A b e l l et al. 2 0 0 2 ) .

Conservation strategies formulated at the ecoregional

scale have the potential to address the fundamental

goals of biodiversity conservation: (1) representation

of all distinct natural communities within conservation

landscapes and protected-area networks; (2) mainte-

nance of ecological and evolutionary processes that

create and sustain biodiversity; (3) maintenance of

viable populations of species; and (4) conservation of

blocks of natural habitat that are large enough to be

resilient to large-scale stochastic and deterministic dis-

turbances as well as to long-term changes. Freshwater

ecoregions have been delineated largely on the basis of

fish distributions and planning approaches incorporat-

ing the broader dynamics of freshwater systems are

evolving (Abell et al. 2003). Areas of future work

include, but are not limited to, designing strategies to

address threats posed by supra-catchment stresses and

by catchment land uses. While supra-catchment

impacts cannot be mitigated through the designation of

traditional protected areas, there is largely untapped

potential to develop protected areas to address terres-

trial impacts.

Based on a review of existing site prioritisation

schemes such as the ecoregion approach, as well as on

consultations with experts, the IUCN Species

Programme has developed an integrative method for

terrestrial, marine and freshwater ecosystems (Darwall

and Vié 2003). Similar approaches are being instituted

in Australia (Dunn 2003), the UK (Boon 2000) and

elsewhere.

Focal species protection

Species-focused conservation measures are

particularly important where threatened species cannot

be conserved through protected areas. This is the case

for many of the large migratory species spending much

of their life cycle outside protected areas and those that

may also be heavily exploited. Species-focused strate-

gies will typically involve multiple measures such as

River fisheries : Ecological basis for management and conservation 37

protection of key habitats and provision of passage

facilities (Galat and Zweimuller 2001), as well as

restrictions on fisheries exploitation. Chang et al.

(2003) used an adaptive learning algorithm, the self-

organizing map (SOM) to pattern the distribution of

endemic fish species found in the Upper Yangtze and

to identify alternative reserve areas for their conserva-

tion.

Mitigation

Attempts to mitigate, rather than remove, exist-

ing threats are probably the most common approach to

conservation of river resources. Most mitigation meas-

ures aim to retain something of the original diversity of

the ecosystem.

Only very limited mitigation or compensation

for supra-catchment effects can be carried out at the

level of aquatic ecosystems, such as liming of water

bodies affected by acid deposition, or management of

regulated rivers to compensate for hydrological effects

of climate change.

A range of mitigation measures is available for

effects of catchment land use and river corridor engi-

neering. These include buffer strips to protect rivers

from direct agricultural runoff, agricultural land and

waste management to minimize erosion and pollution

(Large and Petts 1996). A wide range of habitat protec-

tion and creation techniques have been described

(Cowx and Welcomme 1998), although their effective-

ness in achieving biological conservation objectives

requires further investigation. Details in the design and

operation of dams, weirs and flood control embank-

ments can make a great deal of difference to the

integrity of riverine ecosystems Larinier, Trevade and

Porcher 2002; de Graaf 2002). Much experience is

available now in the design of fishways (Larinier et al.

2002, FAO/DVWK 2002), although this is focused on

temperate climates and the common designs may not

be appropriate for tropical systems. Other measures

include creation of spawning substrate for focal fish

species (e.g. salmonids), instituting fish stocking pro-

grams, providing simulated flood discharges and flush-

ing flows for particular ecological and water quality

objectives (Reiser, Ramey and Lambert 1989) and

implementing more comprehensive flow prescriptions

to protect river ecosystems (for method see Arthington

et al. 2003a and b; King et al. 2003). Maintenance or

restoration of key hydrological patterns is crucial to

conservation and methods for assessing such patterns

are discussed in section 5. Large rivers can be protect-

ed from further deterioration by limiting development

on the floodplains, prohibiting mainstream dams and

limiting activities designed to constrain the main chan-

nel, such as dredging, straightening and hardening of

banks.

Exploitation impacts are addressed by regulat-

ing fishing activities through restrictions on total

effort, gear types and seasonal or spatial closures. In

multi-species fisheries, determining appropriate

exploitation levels is difficult even in principle because

vulnerability to fishing differs greatly between species

that may be harvested fairly indiscriminately by fish-

ing gear. Even moderate levels of overall effort may be

too high for the most vulnerable (usually long-lived)

species, while aggregated yields may be maximized at

much higher effort levels. The inherent problem of

deciding what level of exploitation is sustainable or

desirable (Rochet and Trenkel 2003) is further con-

founded by the practical difficulties of assessing

exploitation status and options in often data-poor

inland fisheries. Methods for assessing exploitation are

reviewed in section 5, while the human aspects of

managing fisheries are dealt with in other chapters of

this volume.

Worldwide, fish introductions and transloca-

tions are strongly restricted by national and interna-

tional laws and codes of conduct. Where such meas-

ures are considered, a risk assessment should be con-

ducted following established frameworks such as those

reviewed by Coates (1998).

38

Rehabilitation and restoration

Rehabilitation and restoration are assuming a

high profile in many countries as an extension of soil

conservation programs and initiatives to improve

water quality. Interventions focused on the morpholo-

gy of river systems are also increasing (Brookes 1992;

Clifford 2001), for instance by restoring portions of the

floodplains by local piercing of dykes, setting back

levees from the main channel and removing revet-

ments and wing dykes from river banks. Many of these

strategies are based on the recognition of the impor-

tance of connected side-arm channels and their role in

sustaining the fish biodiversity of large rivers

(Humphries et al. 1999; Brosse et al. 2003). Adequate

protection and management of riparian zones, based on

sound ecological principles, is another effective strate-

gy for addressing many existing problems of river

ecosystem degradation (Bunn et al. 1993; Kauffman,

Beschta, Otting and Lytjen 1997) and is essential to the

maintenance and management of freshwater fishes

(Pusey and Arthington 2003). However, various stud-

ies have produced conflicting results regarding the rel-

ative impacts to aquatic ecological integrity of land

uses in the riparian zone versus activities in the wider

catchment (Hughes and Hunsaker 2002).

Numerous examples of how these and other

restorative measures have been implemented exist,

principally from developed countries. Among the most

famous is the ongoing restoration of the channelled

Kissimmee River in Florida, which involves integra-

tion of hydrological, hydraulic and water quality prin-

ciples with concepts of ecological integrity (Koebel,

Harris and Arrington 1998). The primary goal of the

project is to re-establish the river’s historical flow

characteristics and its connectivity to the floodplain

(Toth et al. 1993). A method for rehabilitating smaller

rivers has been articulated in the stepwise (“Building

Block”) approach (Petersen et al. 1992) and there is a

growing literature on principles and guidelines for

river corridor restoration (e.g. Ward et al. 2001).

Session 3 Review :

ECOLOGICAL APPROACHES AND TOOLS FOR

MANAGEMENT DECISION SUPPORT

Clearly, the conservation of river ecosystems

and the sustainable exploitation of their fisheries

require integrating ecological knowledge into river and

fisheries management. In this section we review

approaches and tools for making such ecological

knowledge available to management and decision

processes.

The challenge of providing ecological decision

support

There are four important requirements for

effective decision-support tools: (1) tools must be rel-

evant, i.e. they must address the specific issues

encountered by decision makers; (2) tools must be sci-

entifically and ecologically sound, i.e. they must

reflect current knowledge including uncertainties/

ignorance; (3) tools must be practical, i.e. they must be

easily parameterised and understood; and (4) tools

must be appropriate in the context of the decision-mak-

ing process, i.e. they must be usable by some of the

stakeholders involved and should be transparent to

most. Failure of any management approach or tool to

satisfy these criteria will render it ineffective. This

implies that factors such as the degree of stakeholder

participation in management and the extent of local

ecological knowledge are just as important to consider

in the design of decision-support tools as the underly-

ing ecology.

Habitat-centered assessment

Many approaches for assessing ecological

impacts of corridor engineering and other disturbances

focus on habitat availability and suitability rather than

aquatic population abundance or assemblage structure

as such (e.g. Clifford 2001). This reflects the reason-

able (but not always accurate) assumption that popula-

tions are likely to persist as long as habitats are main-

tained. Predicting population or assemblage dynamics

is a complex task and will introduce additional uncer-

River fisheries : Ecological basis for management and conservation 39

tainty, without necessarily producing additional insight

into the problem at hand. However, it is unlikely that

any single assessment of habitat will encompass the

myriad different ways or scales at which habitat is per-

ceived or used by aquatic organisms. There is always

the potential for a habitat-based approach to define a

reach as suitable for one taxon but completely unsuit-

able or less suitable for another and in the case where

the former taxon is critically dependent on the latter, it

is unlikely that a good conservation outcome will be

achieved. The maintenance of a desired proportion of

“optimum habitat” at a series of river reaches may

result in the situation where it is impossible to simulta-

neously accommodate each reach because of spatial

variation in the overarching factor determining habitat

suitability (i.e. discharge). Habitat-centred assessments

may not be sufficiently holistic in outlook to advise

managers strategically.

Nonetheless, habitat approaches have value in

identifying critical elements for individual species. For

example, discharge-based modelling of habitat struc-

ture may be used to identify the magnitude of critical

flow events necessary to allow the passage of migrato-

ry species. In addition, time series of habitat suitabili-

ty based on the flow duration curve may be useful

(Tharme 1996) in assessing the importance (defined by

the frequency of occurrence) of particular conditions

or the desirability of maintaining such conditions. In

her discussion of physical habitat/discharge modelling,

Tharme (1996) recommended that a wide array of

trophic levels be included so as to improve the gener-

ality of habitat-based assessments.

Some larger-scale habitats, such as floodplains,

are accepted as being important to a wide range of

riverine biota. In this case, assessments of habitat

a v a i l a b i l i t y , for example through combinations of

hydrologic and terrain topographic modelling, may

present a useful approach.

Modeling fish populations and assemblages

Empirical models

Empirical models are statistical representations

of variables or relationships of interest, without refer-

ence to underlying processes. Average fisheries yield

per area estimates (e.g. from different habitat types)

may be regarded as the simplest of empirical models,

but can be extremely useful in decision-making about

habitat protection or creation (Jackson and Marmulla

2001; Lorenzen et al. 2003b).

Most empirical models are regression models

that relate parameters such as yield, abundance, or

diversity to one or more factors of interest, usually

exploitation intensity (effort) and/or environmental

characteristics. Regression models are appropriate for

comparative studies involving independent observa-

tions, while time-series models are appropriate where

data are auto-correlated (i.e. time series of observa-

tions from a single system). Fishing intensity tends to

be the single most important factor determining yields

in comparative studies of floodplain rivers (Bayley

1989) and lagoons (Joyeux and Ward 1998). However,

hydrological factors may be dominant in system-spe-

cific models, particularly where fishing effort is either

stable or itself related to hydrology (as in the flood-

plains of Banglasdesh). Empirical models relating

river or estuarine fisheries yields to hydrological vari-

ables such as discharge have been derived for many

systems (e.g. Welcomme 1985; Loneragan and Bunn

1999; de Graaf et al. 2001).

Rule-based and Bayesian network models

Rule-based and Bayesian network models are

logical representations of the relationships between

cause and effect variables, hence they occupy an inter-

mediate position between purely empirical models and

mechanistic (e.g. population dynamics) models. In the

case of Bayesian networks, probability distributions

are attached to all variables and the distributions of

response variables are modified by applying Bayes

40 Session 3 Review :

theorem (Jensen 1996). Bayesian network models for

predicting (co)-management performance are

described by Halls et al. (2001b). These models use

multidisciplinary explanatory variables to predict a

range of performance measures or outcomes, including

sustainability, equity and compliance and are designed

to support adaptive management approaches. Baran,

Makin and Baird (2003) present a Bayesian network

model to assess impacts of environmental factors,

migration patterns and land use options on fisheries

production in the Mekong River. The natural produc-

tion levels that can be expected for each fish group

(black fishes, white fishes and opportunists and three

geographic sectors (Upper Mekong, Tonle Sap system

and the Mekong Delta), are qualitatively expressed by

a percentage between “bad” and “good”. Such a result

can be converted into tons of fish when statistical time

series are available.

Bayesian network models are increasingly

being incorporated into decision support systems for

the determination of river flow regimes that will sus-

tain river ecosystems and their fish populations

(Arthington et al. 2003a and b).

Population dynamics models

Population dynamics models have been central

to decision analysis in marine fisheries management

for a long time, but they have not been widely used in

rivers. This is likely to reflect differences in manage-

ment requirements (annual setting of exploitation tar-

gets in marine fisheries versus more focus on environ-

mental factors and a longer term perspective in fresh-

water systems) and the fact that models developed for

marine fisheries are largely unsuitable for addressing

the river fisheries issues.

The development of models addressing the

linkages between fish populations and abiotic process-

es central to the management of rivers for fisheries

began with Welcomme and Hagborg’s (1977) model.

Over the past few years, there has been an upsurge of

interest in population models for river and floodplain

fish stocks. Halls et al. (2001a) and Halls and

Welcomme (2003) present an age-structured model

incorporating sub-models describing density-depend-

ent growth, mortality and recruitment to explore how

various hydrographical parameters affect the dynamics

of a common floodplain river fishes. The results of the

simulations offer insights into hydrological criteria for

the maintenance of floodplain-river fish faunas and

can be used to design appropriate flooding regimes that

maximise benefits from the water available. Minte-

Vera (2003) developed a lagged recruitment, survival

and growth model (LRSG - Hilborn and Mangel 1997)

for the migratory curimba P r ochilodus lineatus

(Valenciennes 1847) in the high Paraná River Basin

(Brazil), with recruitment as a function of flood and

stock size. Distributions obtained were used to evalu-

ate the risk to the population from various fisheries and

dam-operation management decisions. Lorenzen et al.

(2003a) developed a biomass dynamics model for fish-

eries and hydrological management of floodplain lakes

and reservoirs. The model accounts explicitly for pro-

duction and catchability effects of water area fluctua-

tions. Models of population dynamics in relation to

flow in non-floodplain rivers have been developed by

van Winkle et al. (1998); Jager et al. (1999); Peterson

and Kwak (1989) and Gouraud et al. (2001).

Model development and testing are still at a rel-

atively early stage; more validation is required and the

relative importance of compensatory processes

remains largely uncertain. However, initial results

appear promising, particularly with respect to biomass

dynamics and dynamic pool models. Certainly, densi-

ty-independent effects on fish populations require fur-

ther investigation, particularly the effect of different

flooding patterns on primary and secondary production

per unit area or volume flooded. Other factors such as

the influence of hydrology on processes such as

spawning success need further evaluation and consid-

eration in models of this type.

River fisheries : Ecological basis for management and conservation 41

Many tropical river-floodplain fisheries are

inherently multi-species and multi-gear fisheries. In

such systems it is difficult to manage species in isola-

tion, due to technical and biological interactions.

Technical interactions arise because a range of species

are harvested by the same fishing gear and it is not

therefore possible to optimize exploitation for individ-

ual species independently. Biological interactions arise

from predation and competition. The assessment of

multi-species fisheries remains a major challenge, but

several tools are now available to aid their analysis.

Technical interactions can be analyzed using BEAM4

(Sparre and Willmann 1991) for river fisheries applica-

tions see Hoggarth and Kirkwood (1995). The ECO-

PATH family of models has emerged as widely used

too for assessing biological interactions. Often, how-

ever, data available for river fisheries will be too limit-

ed to allow even simple applications of such models.

Simple and robust indicators for assessing such fish-

eries based on aggregated catch/effort and possibly

size structure or species composition data should

receive more attention. All of the models discussed

above focus on the dynamics of populations at relative-

ly high abundance, where populations are subject to

compensatory density dependence and demographic

stochasticity can be ignored. Such models are impor-

tant to decision-making in fisheries management con-

texts, but the dynamics of populations at risk of extinc-

tion are not captured well. Methods of population via-

bility analysis have been used to prioritize salmon

stocks for conservation (Allendorf et al. 1997), but fur-

ther development of these approaches for freshwater

fish populations is highly desirable.

Integrating information

The integration of biological and environmen-

tal data in models (conceptual, rule-based, statistical,

predictive) is increasingly being used to underpin

audits of aquatic ecosystem health (Bunn, Davies and

Mosisch 1999), in environmental impact assessments

and in river restoration activities (e.g. the restoration of

important characteristics of river flow regimes; Toth,

Arrington, Brady and Muszick 1995; Toth et al. 1997).

The quantification of modified flow regimes that will

maintain or restore biodiversity and key ecological

functions in river systems is increasingly concerned

with the integration of information on river hydrology,

geomorphology, sediment dynamics and ecology, all

linked to the social consequences of changing river

flows (Arthington et al. 2003a and b; King et al. 2003).

The so-called holistic environmental flow methods

that make use of many types of information, including

local ecological knowledge, models and professional

judgement, are the most suitable for large river sys-

tems. Examples include the environmental flow

methodology DRIFT (Downstream Response to

Imposed Flow Transformations) originating in South

Africa (King et al. 2003) and similar A u s t r a l i a n

approaches (Cottingham, Thoms and Quinn 2002;

Arthington and Pusey 2003). For reviews of such

methods and recent innovations see Arthington et al.

(2003a and b) and Tharme (1996, 2003).

Resolving uncertainty

Major theoretical advances have been made in

understanding how large rivers and their fisheries

function, yet the science underlying river and fisheries

management is still beset by fundamental problems of

uncertain knowledge and limited predictive capability

(Poff et al. 2003). Uncertainly arises both from irre-

ducible ecosystem complexity and from uncertain

transferability of general ecological understanding to

specific situations. Uncertainty is such a pervasive fac-

tor in ecological management that it must be dealt with

explicitly and constructively by, we suggest, process

research and tools such as adaptive management,

strategic assessment and meta-analysis.

Process research

More research on many of the key ecological

processes discussed above is clearly warranted (see

priorities discussed below), but this will take time and

may not reduce uncertainty enough to allow reliable

predictions at the scale required for management deci-

sion-making.

42

Adaptive management

In the long term we may reduce uncertainty and

increase the effectiveness of management measures, if

their consequences are monitored and management

measures adapted accordingly. Adaptive management

is a process of systematic “learning by doing” (Walters

1997). It involves three main aspects: (1) uncertainty is

made explicit, (2) management measures are consid-

ered as experiments, designed to yield information as

well as material benefits and (3) management meas-

ures and procedures are modified in light of results

from management experiments. Adaptive management

may be implemented within just a single site, but it is

often advantageous to work across a number of similar

sites in order to increase replication and, possibly, test

a range of management options in parallel, thus

achieving results more quickly than through sequential

experimentation. The costs of adequate monitoring can

be considerable and therefore experimental manage-

ment should be considered only where the costs of the

intervention or the anticipated benefits warrant this

expenditure.

Strategic assessment and meta-analysis

Strategic assessments of impacts or mitigation

measures synthesize results from individual projects as

well as wider relevant knowledge. Strategic assess-

ments carried out on a national or regional basis are

likely to improve the effectiveness of future assess-

ments and management interventions substantially.

Meta-analysis is an approach increasingly used to syn-

thesize and integrate ecological research conducted in

separate experiments and holds great promise for iden-

tifying key factors affecting river ecosystems and

e ffective conservation measures (Arnqvist and

Wooster 1995; Halls et al. 2001b). Fuzzy Cognitive

Mapping (Hobbs et al. 2002) is a promising new tech-

nique for integrating disconnected case studies to

guide ecosystem management. Bayesian networks,

which express complex system behaviour probabilisti-

cally, can facilitate predictive modelling based on

knowledge and judgement, thereby enhancing basic

Session 3 Review :

understanding without the requirement of excessive

detail (e.g. Reckhow 1999).

SUMMARY AND RECOMMENDATIONS

Although major advances have been achieved

across the broad field of river ecology and fisheries,

substantial information gaps characterize every funda-

mental aspect of fish biology and the ecological

processes sustaining fisheries in large river systems.

Here we summarize the major points and conclusions

arising from our review and the discussions held dur-

ing LARS 2, beginning with general statements intend-

ed to emphasize the importance of healthy rivers and

their fisheries. The main research priorities identified

in this review are given emphasis (see also Dugan et

al. 2002).

Large rivers and their floodplains provide a

wide range of ecosystem goods and services to socie-

ty. Many of these services, fisheries production in par-

ticular, depend upon the biodiversity and ecological

integrity of aquatic ecosystems. The harnessing, devel-

opment and management of rivers and their natural

resources have contributed to economic development

for some segments of society, but usually such devel-

opment is accompanied by severe degradation of eco-

logical integrity. There is evidence that the true value

of fisheries has often been underestimated compared to

the value of river development.

Biodiversity of large rivers are threatened by

climate change, deforestation, agricultural and urban

land use, pollution, channel modifications, inter-basin

transfers of water and modified flow regimes, loss of

habitat and habitat connectivity, introduced species

and fishing pressure. These impacts are of particular

concern in tropical floodplain rivers, which are home

to over 50 percent of the world’s freshwater fish

species. There is a critical need to define the factors

and processes that maintain biodiversity and ecosys-

tem services at river basin and regional scales.

River fisheries : Ecological basis for management and conservation 43

Tropical floodplain rivers present a rare oppor-

tunity to conserve important areas of biological diver-

sity and aquatic resources before they deteriorate under

pressure from development. The conservation of

important genetic stocks, species and species complex-

es is a priority. Methods are evolving to define conser-

vation and restoration priorities in large rivers but the-

oretical and methodological considerations merit more

attention (Abell 2002). Major data gaps for species dis-

tributions prevent identification of hotspots for rich-

ness, endemism and other conservation targets, hinder-

ing effective conservation planning. Further, planners

are challenged to design strategies that will maintain

the often large-scale abiotic and biotic processes that

shape habitats and support the persistence of biodiver-

sity.

In many cases, the maintenance of healthy river

ecosystems and all components of biodiversity

(species, genetic stocks, ecological and evolutionary

processes) are synonymous with maintaining healthy

productive fisheries and sustaining livelihoods.

Occasionally, however, modified systems can provide

high levels of fishery production (e.g. via stock

enhancement programs in modified habitats, particu-

larly water storage reservoirs) even though their biodi-

versity is compromised. Hence, it is important to dis-

tinguish clearly between fisheries production and con-

servation aspects of rivers where the former are impor-

tant, particularly in a developing country context.

Natural flow regimes and hydrological vari-

ability (quantity, timing and duration of flows and

floods and periods of low flows) are considered essen-

tial for maintaining biodiversity and fisheries, espe-

cially in strongly seasonal river systems (Poff et al.

1997). The Flood Pulse Concept (Junk et al. 1989)

remains a robust and widely applicable paradigm in

tropical floodplain rivers with predictable annual flood

pulses, governing maintenance of biodiversity, energy

flow and fisheries productivity. Maintaining the annu-

al flood pulse in tropical floodplain rivers and the vari-

able patterns of flows and floods in rivers with more

erratic flow regimes should be the first priority in

water management.

Research on flow-ecological relationships in

large rivers and further development of conceptual,

empirical and dynamic ecological models, are urgent

research priorities (Arthington and Pusey 2003).

Interim environmental flow prescriptions should be set

now, in major rivers of conservation concern and those

sustaining fisheries and livelihoods. Holistic ecosys-

tem environmental flow methods such as DRIFT (King

et al. 2003) and its fish component (Arthington et al.

2003a), using all information, including local ecologi-

cal knowledge, models and professional judgement,

are the most suitable methods for defining flow

regimes in large river systems.

Sustaining river ecosystems and productive

fisheries depends in part upon understanding the ener-

getic basis of their productivity, linked to the trophic

ecology of fish and food web structure. Food webs in

large rivers are complex and influenced by many abi-

otic and biotic factors. Nevertheless, to inform man-

agement, we need a food web perspective on multi-

species fisheries in large rivers, because stock dynam-

ics are influenced by both bottom-up factors related to

ecosystem productivity and by top-down factors influ-

enced by relative densities of predator and prey popu-

lations. Research into the productive basis of fish pop-

ulations and fisheries in different habitats is a priority

(Winemiller 2003).

There is evidence of ecosystem overfishing in

many tropical rivers and large long-lived species are

endangered as a result. The implications of “fishing

down the food web” (Pauly et al. 1998) and species

loss for the sustainability, variability and management

of fisheries, as well as for biodiversity protection, need

to be explored further.

44 Session 3 Review :

More research is required to understand basin-

wide threat mechanisms, interactions and scales of

response. Mitigation measures include the restoration

of hydrological and sediment dynamics, riparian vege-

tation, river habitat diversity and floodplain connectiv-

ity (Tockner and Stanford 2002). More investment in

monitoring and evaluation is required to determine the

success of such efforts.

For most large river systems, essential informa-

tion is lacking on biodiversity (of all aquatic biota),

species distributions and habitat requirements of fish-

es, migration and spawning cues, all aspects of migra-

tion patterns, reproductive biology and population

dynamics. Habitat (in its very broadest sense) may be

used in assessments of ecological integrity, in quanti-

fying environmental flows and in planning conserva-

tion strategies, as a surrogate for biotic requirements

where data on the latter are limited. If habitat-based

assessments must be used, a wide array of trophic lev-

els should be included to improve the generality of

habitat-based assessments (Tharme 1996).

Quantitative measures at the population level

(yield, abundance, extinction risk) are important for

decision-making on many issues, including trade-offs

between water resources development and fisheries.

Despite some fundamental gaps in ecological knowl-

edge (e.g. the basis of floodplain production), fisheries

models accounting for hydrological variability and

exploitation impacts on large populations are becom-

ing available and will allow a more detailed analysis of

water management-fisheries interactions (Halls and

Welcomme 2003). Further elucidating density-depend-

ent and density-independent mechanisms that regulate

and determine fish abundance is a key challenge.

Understanding of proximate mechanisms underlying

life history plasticity (including migration cues)

requires further research.

A significant gap is the lack of data, theory and

models for small and endangered populations where

demographic stochasticity, depensation and metapopu-

lation structure are significant factors in dynamics.

This area should be addressed as a matter of priority,

given the imperilled status of a significant proportion

of riverine biota.

Major theoretical advances have been made in

understanding how large rivers and their fisheries

function. Further development of ecological theory for

river biota and fisheries will provide a better basis for

management and conservation in the longer term. This

will require integration of field data collection, man-

agement experiments (i.e. “learning by doing” Walters

1997) and modelling.

Routine fisheries data collection should be

focused more strongly on providing information rele-

vant to key issues in river management. This will

require a closer link between research, management

and administration. Modelling should play a key role

in synthesising information, formulating and testing

hypotheses and improving data collection, experimen-

tal design and management actions.

Despite recent advances, the science underly-

ing river and fisheries management is still beset by

fundamental problems of uncertain knowledge and

limited predictive capability (Bunn and Arthington

2002). Uncertainty arises both from irreducible

ecosystem complexity and from uncertain transferabil-

ity of general ecological understanding to specific sit-

uations (Poff et al. 2003). Uncertainty is such a perva-

sive factor in ecological management that it must be

dealt with explicitly and constructively.

Adaptive management will often be the most

effective way of resolving uncertainties, improving

management and generating key ecological knowl-

edge. Well-planned management experiments should

be carried out and comprehensively documented far

more widely than hitherto (Poff et al. 2003).

River fisheries : Ecological basis for management and conservation 45

Meta-analysis also holds great potential to

answer key ecological questions from the combined

analysis of studies on individual sites and river basins.

Studies in individual systems should report averages as

well as variability, minimum and maximum values, to

be amenable for inclusion in such quantitative synthe-

ses. A paucity of comparative analyses was a conspic-

uous gap in papers submitted to LARS 2.

Already a range of modelling tools is available

to support decision-making in river basin and fisheries

management. Risk assessment can provide a frame-

work for decision-making by explicitly including

uncertainties, data and previous knowledge in quanti-

tative frameworks. Modelling approaches can facilitate

communication between stakeholders.

Beyond general principles at the conceptual

level and volumes of international recommendations,

there is a dearth of practical guidelines for managers to

apply at the operational level. There are also few tools

to help stakeholders assess various management

options and trade-offs. A compendium of decision

tools for river ecological and fisheries management

should be compiled and maintained, to provide man-

agers, stakeholders and decision makers with an up-to-

date guide to available resources.

Conspicuous gaps at LARS 2 concern the eco-

logical linkages between uplands, rivers, lowland

floodplains, estuaries and coastal systems, even though

recent research has highlighted the importance of

flow-related and land-based processes affecting estuar-

ine ecosystems and their fish stocks. The ecological

roles of groundwater and surface-groundwater

processes and the consequences of climate change for

aquatic ecosystems and fisheries, also received very

little attention in submitted papers. The design of fish-

ery management practices, environmental flows,

restoration strategies and conservation reserves to cope

with potential impacts of climate change is a largely

unexplored research frontier.

REFERENCES

Abell R. 2002. Conservation biology for the biodiversity

crisis: A freshwater follow-up. Conservation

Biology, 16: 1435-1437.

Abell R., Thieme M., Dinerstein E., & Olson D. 2002. A

sourcebook for conducting biological assess -

ments and developing biodiversity visions for

e c o r egion conservation . Vo lu me II:

F r eshwater ecore g i o n s . Washington, DC,

World Wildlife Fund. 201 pp.

Abell R., Thieme M. & Lehner B. 2003. Ecoregion con-

servation for freshwater systems, with a focus

on large rivers. In R.L. Welcomme & T. Petr,

eds. Proceedings of the Second International

Symposium on the Management of Larg e

Rivers for Fisheries Volume 1 . Phnom Penh,

Mekong River Commission.

Agostinho A. & Gomes L.C. 2003. Fisheries management

in the upper Paraná River Basin: Successes and

failures. In R.L. Welcomme & T. Petr. eds.

P r oceedings of the Second International

Symposium on the Management of Larg e

Rivers for Fisheries Volume 1 . Phnom Penh,

Mekong River Commission.

Allendorf F.W., Bayles D., Bottom D.L., Currens K.P.,

Frissell C.A., Hankin D., Lichatowich J.A.,

Nehlsen W., Trotter P.C. & Williams T.H.

1997. Prioritizing Pacific salmon stocks for

conservation. Conservation Biology, 11: 140-

152.

Almeida O.T., Lorenzen K. & McGrath D.G. 2002.

Impact of co-management agreements on the

exploitation and productivity of floodplain

lake fisheries in the lower Amazon. Procee-

dings of the ninth international conference of

the IASCP. (Available at http://dlc.dlib.indi-

a n a . e d u / d o c u m e n t s / d i r 0 / 0 0 / 0 0 / 0 7 / 8 2 / d l c -

00000782-00/almeidao080502.pdf )

46

Aparico E., Vargas M.J., Olmo J.M & de Sostoa A. 2000.

Decline of native freshwater fishes in a

Mediterranean watershed on the Iberian

Peninsula: A quantitative assessment.

Environmental Biology of Fishes, 59: 11-19.

Arlinghaus R., Mehner T. & Cowx I.G. 2002.

Reconciling traditional inland fisheries man-

agement and sustainability in industrialized

countries, with emphasis on Europe. Fish and

Fisheries, 3: 261-316.

Arnkvist G. & Wooster D. 1995. Meta-analysis:

Synthesizing research findings in ecology and

evolution. Trends in Ecology and Evolution,

10: 236-240.

Arrington D.A. & Jepsen D.B. 2001. Evaluation of

ecosystem enhancement using growth rates of

Centrarchid fishes. Florida Scientist, 64: 197-

215.

Arrington D.A. & Winemiller K.O. 2003. Organization

and maintenance of biological diversity in

neotropical floodplain rivers. In R . L .

Welcomme & T. Petr. eds. Proceedings of the

Second International Symposium on the

Management of Large Rivers for Fisheries

Volume 1 . Phnom Penh, Mekong River

Commission.

Arthington A.H. 1991. The ecological and genetic

impacts of introduced freshwater fishes in

Australia. Canadian Journal of Fisheries and

Aquatic Sciences Suppl. 48, 1: 33-44.

Arthington A.H. & Bluhdorn D.R. 1994. Distribution,

genetics, ecology and status of the introduced

cichlid, O r e o c h r omis mossambicus, in

Australia. In D. Dudgeon & P. Lam, eds.

Inland waters of tropical Asia and Australia:

Conservation and Management. Mitteilungen

Communications, Societas Internationalis

Limnologiae SIL, 24: 53-62.

Session 3 Review :

Arthington A.H. & Bluhdorn D.R. 1996. The effects of

species interactions resulting from aquaculture

operations. In D.J. Baird, M.C. Beveridge,

L.A. Kelly & J.F. Muir, eds. Aquaculture and

water re s o u r ce management. Oxford, UK,

Blackwell Science. pp. 114-138.

Arthington A.H., Tharme R.E., Brizga S.O., Pusey B.J. &

Kennard M.J. 2003b. Environmental flows:

Ecological importance, methods and future

challenges. In R.L. Welcomme & T. Petr. eds.

P r oceedings of the Second International

Symposium on the Management of Larg e

Rivers for Fisheries Volume 1. Phnom Penh,

Mekong River Commission.

Arthington A.H., Hamlet S. & Bluhdorn D.R. 1990. The

role of habitat disturbance in the establishment

of introduced warm-water fishes in Australia.

In D.A. Pollard ed. Introduced and translocat -

ed fishes and their ecological effects.

P r oceedings No. 8, pp. 61-66. Canberra,

Bureau of Rural Resources, Australian Govt.

Pub. Service.

Arthington A.H., King J.M., O’Keefe J.H., Bunn S.E.,

Day J.A., Pusey B.J., Bluhdorn D.R. &

Tharme R. 1992. Development of an holistic

approach for assessing environmental flow

requirements of riverine ecosystems. In J.J.

Pigram and B.P. Hooper, eds. P roceedings of

an international seminar and workshop on

wa ter allo ca tion for the enviro n m e n t .

Armidale, Centre for Water Policy Research,

University of New England. pp. 69-76.

Arthington A.H. & Pusey B.J. 2003. Flow restoration and

protection in Australian rivers. River Research

and Applications, 19: 1-19.

Arthington A.H., Rall J.L., Kennard M.J. & Pusey B.J.

2003a. Environmental flow requirements of

fish in Lesotho rivers using the DRIFT

m e t h o d o l o g y . River Research and

Applications, 19.

River fisheries : Ecological basis for management and conservation 47

Arthington A.H. & Welcomme R.L. 1995. The condition

of large river systems of the world. In C.W.

Voigtlander ed. Proceedings of the world fish -

eries congress. New Delhi, Oxford and IBH

Publishing Co. Pty Ltd. pp. 44-75.

Bain M.B. & Stevenson N.J. 1999. Aquatic Habitat

Assessment: Common Methods. B e t h e s d a ,

Maryland: American Fisheries Society.

Baird D.J., Beveridge M.C., Kelly L.A. & Muir J.F. 1996.

A q u a c u l t u r e and Water Resourc e

Management. Oxford, UK, Blackwell Science.

Baird I.G. & Flaherty M.S. 2003. Beyond national bor-

ders: Links between an important Mekong

River medium sized migratory carp fishery

below the Khone Falls in southern Laos and

bag net fisheries at stream mouths in northeast

Cambodia. Abstract submitted to the Second

International Symposium on the Management

of Large Rivers for Fisheries. Phnom Penh,

Mekong River Commission.

Baird I.G., Flaherty M.S. & Phylavanh B. 2000. Rhythms

of the river: Lunar phases and small cyprinid

migrations in the Mekong River. Champassak

Province, Lao PDR, CESVI Project for envi-

ronmental protection and community develop-

ment in the Siphandone wetland. 42 pp.

Baran E., Makin I. & Baird I.G. 2003. Bayfish: A model

of environmental factors driving fish produc-

tion in the lower Mekong Basin. In R . L .

Welcomme & T. Petr. eds. Proceedings of the

Second International Symposium on the

Management of Large Rivers for Fisheries

Volume 2. Phnom Penh, Mekong River

Commission.

Barbarino Duque A., Taphorn D.C. & Winemiller K.O.

1998. Ecology of the coporo, P r o c h i l o d u s

mariae Characiformes, Prochilodontidae and

status of annual migrations in western

Venezuela. Environmental Biology of Fishes,

53: 33-46.

Barlow C.G., Hogan A.E. and Rogers L.G. 1987.

Implications of translocated fishes in the

apparent extinctions in the wild of the Lake

Eacham rainbowfish, Melanotaenia

eachamensis. Australian Journal of Marine

and Freshwater Research, 38: 897-902.

Bayley P.B. 1988a. Accounting for effort when compar-

ing tropical fisheries in lakes, river-floodplains

and lagoons. Limnology & Oceanography, 33:

963-972.

Bayley P.B. 1988b. Factors affecting growth rates of

young tropical floodplain fishes - seasonality

and density- de pendence. E n v i r o n m e n t a l

Biology of Fishes, 21: 127-142.

Bayley P.B. 1989. Aquatic environments in the Amazon

Basin, with an analysis of carbon sources, fish

production, and yield. Special Publication of

the Canadian Journal of Fisheries and Aquatic

Sciences, 106: 399-408.

Boisneau & Mennesson-Boisneau 2003. Conservation

strategies for diadromous fishes in Loire River

France. Abstract submitted to the Second

International Symposium on the Management

of Large Rivers for Fisheries. Phnom Penh,

Mekong River Commission.

Boon P.J. 2000. The development of integrated methods

for assessing river conservation value.

Hydrobiologia, 422/423: 413-428.

Boon P.J., Calow P. & Petts G.E. eds. 1992. River

Conservation and Management. Chichester,

UK, John Wiley and Sons. 470 pp.

Bovee K.D. 1982. A guide to stream habitat analysis

using the instream flow incremental methodol -

ogy. Instream Flow Information, Paper 12.

Fort Collins, U.S. Department of Fisheries and

Wildlife Service.

48

Bridges E.M., Ross D.G. & Thompson C.H. 1990. Soils

of the Mary River alluvia near Gympie,

Queensland. CSIRO Division of Soils,

Divisional Report No. 109. 29 pp.

Brizga S.O., Arthington A.H., Pusey B.J., Kennard M.J.,

Mackay S.J., Werren G.L., Craigie N.M. &

Choy S.J. 2002. Benchmarking, a ‘top-down’

methodology for assessing environmental

flows in Australian rivers. P r oceedings of

international conference on enviro n m e n t a l

flows for rivers. Cape Town, SA, University of

Cape Town. (available on CD)

Brookes A. 1992. Recovery and restoration of some engi-

neered British river channels. In P.J. Boon, P.

Calow & G.E. Petts, eds. River conservation

and management. Chichester, UK, John Wiley

and Sons. pp. 337-352.

Brocksen R.W. & Wisniewski J. 1988. Restoration of

aquatic and terrestrial systems. Dordrecht,

Kluwer Academic Publishers. 501 pp.

Brosse S., Lim P. & Lek S. 2003. Biodiversity conserva-

tion in the Garonne River France: Importance

of side-arm channels and floodplain areas.

Abstract submitted to the Second International

Symposium on the Management of Larg e

Rivers for Fisheries. Phnom Penh, Mekong

River Commission.

Bunn S.E., Pusey B.J. & Price P. eds. 1993. Ecology and

management of riparian zones. Canberra,

Land and Water Resource Research and

Development Corporation Occasional Paper

Series No. 5/93. 140 pp.

Bunn S.E., Davies P.M. & Mosisch T.D. 1999. Ecosystem

measures of river health and their response to

riparian and catchment clearing. Freshwater

Biology, 41: 333-346.

Session 3 Review :

Bunn S.E. & Arthington A.H. 2002. Basic principles and

ecological consequences of altered flow

regimes for aquatic biodiversity. Environmen-

tal Management, 30: 492-507.

Bunn S.E., Davies P.M. & Winning M. 2003. Sources of

organic carbon supporting the food web of an

arid-zone flood plain river. F r e s h w a t e r

Biology, 48: 1-17.

Bunn S.E. & Hughes J.M. 1997. Dispersal and recruit-

ment in streams: Evidence from genetic stud-

ies. Jo urna l of the No rth A n m e r i c a n

Benthological Society, 162: 338-346.

Carvalho de Lima A. & Araujo-Lima C.A.R.M. 2003.

Spawning migrations of characiform fishes in

relation to water quality in rivers of the

Amazon. Abstract submitted to the Second

International Symposium on the Management

of Large Rivers for Fisheries. Phnom Penh,

Mekong River Commission.

Chang J., Park Young-Seuk & Lek S. 2003. Conservation

of endemic fishes in Upper Yangtze River,

China. Abstract submitted to the Second

International Symposium on the Management

of Large Rivers for Fisheries. Phnom Penh,

Mekong River Commission.

Clifford N.J. 2001. Conservation and the river channel

environment. In A. Warren & J.R. French, eds.

Habitat conservation: Managing the physical

environment. New York, John Wiley & Sons.

pp. 67-104.

Coates D. 1998. Codes of practice for the stocking and

introduction of fish. In I.G. Cowx, ed. Stocking

and introduction of fish. Oxford, UK,

Blackwell Science. pp. 383-396.

Cottingham P., Thoms M.C. & Quinn G.P. 2002.

Scientific panels and their use in environmen-

tal flow assessment in Australia. Australian

Journal of Water Resources, 5: 103-111.

River fisheries : Ecological basis for management and conservation 49

Crook D.A. & Robertson A.I. 1999. Relationships

between riverine fish and woody debris:

Implications for lowland rivers. Marine and

Freshwater Research, 50: 941-953.

Cowx I.G. 199 4. Stoc king strategies. F i s h e r i e s

Management and Ecology, 1: 15-31.

Cowx I.G. & Welcomme R.L. eds. 1998. Rehabilitation

of Rivers for Fish. Oxford, UK, Blackwells,

268 pp.

Cummins K.W. 1992. Catchment characteristics and river

ecosystems. In P.J. Boon, P. Calow and G.E.

Petts, eds. River Conservation and Manage-

ment. Chichester, UK, John Wiley and Sons.

pp. 125-135.

Cushing D.H. 1990. Plankton production and year-class

strength in fish populations: An update of the

match-mismatch hypothesis. Advances in

Marine Biology, 26: 249-293.

Darwall W.R.T. & Vié J.C. 2003. Identifying important

freshwater biodiversity sites. Abstract submit -

ted to the Second International Symposium on

the Management of Large Rivers for Fisheries.

Phnom Penh, Mekong River Commission.

Das B.P. 2003. Socio economic issues of riverine fish-

eries in India: Impact of fish passes at barriers.

In R.L. Welcomme & T. Petr. eds. Proceedings

of the Second International Symposium on the

Management of Large Rivers for Fisheries

Volume 2. Phnom Penh, Mekong River

Commission.

Davies B.R., Thoms M. & Meador M. 1992. An assess-

ment of the ecological implications of inter-

basin water transfers and their threats to river

basin integrity a nd conser va tion. A q u a t i c

Conservation Marine and Freshwater Systems,

2: 325-349.

De Graaf G., Born B., Kamal Uddin A.M. & Marttin F.

2001. Floods, fish and fishermen. Dhaka, The

University Press Ltd. 110 pp.

Denney, N.H., Jennings, S. & Reynolds, J.D. 2002. Life-

history correlates of maximum population

growth rates in marine fishes. Proceedings of

the Royal Society of London, Series B -

Biological Sciences, 269: 2229-2237.

Detenbeck N.E., DeVore P.W., Niemi G.J. & Lima A.

1992. Recovery of temperate-stream fish com-

munities from disturbance: A review of case

studies and synthesis of theory. Environmental

Management, 16: 33-53.

Dettmers J.M., Wahl D.H., Soluk D.A. & Gutreuter S.

2001. Life in the fast lane: Fish and foodweb

structure in the main channel of large rivers.

Journal of the North Anmerican Benthological

Society, 202: 255-265.

Dudgeon D. 2000. The ecology of tropical Asian rivers

and streams in relation to biodiversity conser-

vation. Annual Review of Ecology and

Systematics, 31: 239-263.

Dugan P.J., Baran E., Tharme R., Prein M., Ahmed M.,

Amerasinghe P., Bueno P., Brown C., Dey M.,

Jayasinghe G. , Niasse M., Nielan d A . ,

Smakhtin V. , Tinh N., Viswanathan K. and

Welcomme R. 2002. The contribution of

aquatic ecosystems and fisheries to food secu-

rity and livelihoods: A research agenda. In

B a c k g r ound papers of the challenge pro -

gramme on water and food. CGIAR. pp. 87-

113.

Dunham J.B. & Rieman B.E. 1999. Metapopulation

structure of bull trout: Influences of physical,

biotic, and geometrical landscape characteris-

tics. Ecological Applications, 9: 642-655.

Dunn H. 2003. Can conservation assessment criteria

developed for terrestrial systems be applied to

riverine systems? Aquatic Ecosystem Health

and Management, 61: 81-95.

50

Dynesius M. & Nilsson C. 1994. Fragmentation and flow

regulation of river systems in the Northern 3rd

of the world. Science, 266: 53-762.

Elwood, J.W., Newbold, J.D., O’Neill, R.V., van Winkle,

W. 1983. Resource spiralling: An operational

paradigm for analyzing lotic systems. In T.D.

Fontaine III, S.M. Bartell, eds. Dynamics of

Lotic Ecosystems. Ann A r b o r , Ann A r b o r

Science Publ. pp. 3-27.

Fagan, W. F . 2002. Connectivity, fragmentation, and

extinction risk in dendritic metapopulations.

Ecology, 83: 3243-3249.

FAO 2000. The state of fisheries and aquaculture. Rome,

FAO.

FAO/DVWK 2002. Fish passes-design, dimensions and

monitoring. Rome, FAO. 119 pp.

Faisal I.M. 2003. Managing international rivers in the

GBM Region: Indo-Bangladesh perspectives.

Abstract submitted to the Second International

Symposium on the Management of Larg e

Rivers for Fisheries. Phnom Penh, Mekong

River Commission.

Fashchevsky, B. 2003. Anthropogenic activities and fish-

eries in the Ponto-Caspian rivers. In R . L .

Welcomme & T. Petr. eds. Proceedings of the

Second International Symposium on the

Management of Large Rivers for Fisheries

Volume 1. Phnom Penh, Mekong River

Commission.

Frissell C.A. 1997. Ecological principles. I n J . E .

Williams, C.A. Wood & M.P. Dombeck, eds.

Watershed restoration: Principles and prac -

tices. American Bethesda, Maryland, Fisheries

Society. pp. 96-115.

Session 3 Review :

Frissell C.A., Liss W.J., Warren C.E. & Hurley, M.D.

1986. A hierarchical framework for stream

habitat classification: Viewing streams in a

watershed context. E n v i r onmental Manage-

ment, 10: 199-214.

Fu Cuizhang, Wu Jihua, Chen Jiakuan, Wu Qianhong &

Lei Guangchun 2003. Freshwater fish biodi-

versity in the Yangtze River Basin of China:

Patterns, threats and conservation. Abstract

submitted to the Second International

Symposium on the Management of Larg e

Rivers for Fisheries. Phnom Penh, Mekong

River Commission.

Galat D.L. & Zweimuller I. 2001. Conserving large-river

fishes: Is the highway analogy an appropriate

paradigm? Journal of the North A m e r i c a n

Benthological Society, 202: 266-279.

Gopal B. 2003. State of degradation and approaches to

restoration of floodplain rivers in India. In R.L.

Welcomme & T. Petr. eds. Proceedings of the

Second International Symposium on the

Management of Large Rivers for Fisheries

Volume 2. Phnom Penh, Mekong River

Commission.

Gotelli N.J. & Taylor C.M. 1999. Testing metapopulation

models with stream-fish assemblages.

Evolutionary Ecology Research, 1: 835-845.

Gouraud V. , Bagliniere J.L., Baran P., Sabaton C., Lim P.

& Ombredane D. 2001. Factors regulating

brown trout populations in two French rivers:

Application of a dynamic population model.

Regulated Rivers Research & Management,

17: 557-569.

Gregory S.V., Swanson F.J., McKee W.A. & Cummins

K.W. 1991. An ecosystem perspective of ripar-

ian zones. BioScience, 41: 540-551.

River fisheries : Ecological basis for management and conservation 51

Gross M.T., Coleman R.M. & McDowall R.M. 1988.

Aquatic productivity and the evolution of

diadromous fish migration. S c i e n c e , 239:

1291-1293.

Groves C.R., D.B. Jensen L.L. Valutis K.H. Redford M.L.

S h a f fer J.M. Scott J.V. Baumgartner J.V.

Higgins M.W. Beck & Anderson M.G. 2002.

Planning for biodiversity conservation: Putting

conservation science into practice. BioScience,

52: 499-512.

Guegan J.F., Lek S. & Oberdorff T. 1998. Energy avail-

ability and habitat heterogeneity predict global

riverine fish diversity. Nature, 391: 382-384.

Halls A.S. 1998. An assessment of the impact of

hydraulic engineering on floodplain fisheries

and species assemblages in Bangladesh.

University of London, 526 pp. (Doctoral dis-

sertation)

Halls A.S., Hoggarth D.D. & Debnath K. 1998. Impacts

of flood control schemes on river fish migra-

tions and species assemblages in Bangladesh.

Journal of Fisheries Biology, 53 Suppl. A:

358-380.

Halls A.S., Debnath K., Kirkwood G.P. & Payne A.I.

2000. Density-dependent recruitment of

Puntius sophore in floodplain waterbodies in

Bangladesh. J. Fish. Biol, 56: 915-922.

Halls A.S., Kirkwood G.P. & Payne A.I. 2001. A dynam-

ic pool model for floodplain river fisheries.

Ecohydrology and Hydrobiology, 1: 323-339.

Halls A.S., Burn R. & Abeyasekera S. 2001b.

Interdisciplinary multivariate analysis for

adaptiv e co-managem ent. Fina l Te c h n i c a l

R e p o r t S ubmitted to the De partme nt for

International Development. 171 pp.

Halls A.S. & Welcomme R.L. 2003. Dynamics of river

fish populations in response to hydrological

conditions: A simulation study. Abstract sub -

mitted to the Second International Symposium

on the Management of Large Rivers for

Fisheries. Phnom Penh, Mekong River

Commission.

Harris J.H. & Gehrke P.C. 1994. Development of predic-

tive models linking fish population recruitment

with streamflow. I n D.A. Hancock ed.

Population dynamics for fisheries manage -

ment. pp. 195-199. Camberra, Bureau of Rural

Resources Proceedings, Australian Govern-

ment Printing Service.

Harrison I.J. & Stiassny M.L.J. 1999. The quiet crisis: A

preliminary listing of the freshwater fishes of

the World that are extinct or “missing in

action.” In R.D.E. MacPhee ed. Extinctions in

near time: Causes, contexts, and conse -

q u e n c e s . New York: Kluwer A c a d e m i c /

Plenum Publishers. pp. 271-332.

Hickley P. & Bailey R.G. 1987. Fish communities in the

eastern seasonal floodplain of the Sudd, south-

ern Sudan. Hydrobiologia, 144: 243-250.

Hilborn R. & Mangel M. 1997. The ecological detective.

Princeton: Princeton University Press. 315 pp.

Hobbs B.F., Ludsin S.A., Knight R.L., Ryan P. A . ,

Biberhofer J. & Ciborowski J.J.H. 2002. Fuzzy

cognitive mapping as a tool to define manage-

ment objectives for complex ecosystems.

Ecological Applications, 12: 1548-1565.

Hogan Z. 2003. The conservation of endangered giant

fish in the Mekong River Basin. Abstract sub -

mitted to the Second International Symposium

on the Management of Large Rivers for

Fisheries. Phnom Penh, Mekong River

Commission.

52

Hoggarth, D.D. & Kirkwood, G.P. 1995. Technical inter-

actions in floodplain fisheries of south and

south-east Asia. I n I.G. Cowx, ed. S t o c k

assessment in inland fisheries. Oxford, UK,

Fishing News Books. pp. 280-292.

Hoggarth D.D., Halls A.S., Dam R.K. & Debnath K.

1999. Recruitment sources for fish stocks

inside a floodplain river impoundment in

Bangladesh. Fisheries Management and

Ecology, 6: 287-310.

Hughes R.M. & Hunsaker C.T. 2002. Effects of land-

scape change on aquatic biodiversity and

biointegrity. In K.J. Gutzwiller, ed. Applying

landscape ecology in biological conservation.

New York, Springer-Verlag. pp. 309-329.

Hugueny B. 1989. West African rivers as biogeographic

islands. Oecologia, 79: 235-243.

Humphries P., King A.J. & Koehn J.D. 1999. Fish, flows

and floodplains: Links between freshwater

fishes and their environment in the Murray-

Darling River system, Australia. Environmen-

tal Biology of Fishes, 56: 129-151.

Huxel G.R. & McCann K. 1998. Food web stability: The

influence of trophic flows across habitats.

American Naturalist, 152: 460-469.

IUCN Species Survival Commission 2000. 2000 IUCN

Red List of threatened species. (Available at:

http://www.iucn.org/redlist/2000/index.html)

Jackson D.C. & Marmulla, G. 2001. The influence of

dams on river fisheries. FAO Fisheries

Technical Paper, 419: 1-44.

Jager H.I., Chandler J.A., Lepla K.B. & van Winkle W.

2001. A theoretical study of river fragmenta-

tion by dams and its effects on white sturgeon

populations. Environmental Biology of Fishes,

60: 347-361.

Session 3 Review :

Jager H.I., van Winkl, W. & Holcomb B.D. 1999. Would

hydrologic climate changes in Sierra Nevada

streams influence trout persistence?

Transactions of the American Fisheries

Society, 128: 222-240

Jefferies R.L. 2000. Allochthonous inputs: Integrating

population changes and food-web dynamics.

Trends in Ecology and Evolution, 15: 19-22.

Jenkins T.M., Diehl S., Kratz K.W. & Cooper S.D. 1999.

Effects of population density on individual

growth of brown trout in streams. Ecology, 80:

941-956.

Jensen F.V. 1996. An introduction to Bayesian networks.

London, UCL Press. 178 pp.

Jordan F.J. & Arrington D.A. 2001. Weak trophic interac-

tions between large predatory fish and herpeto-

fauna in the channelized Kissimmee River,

Florida, USA. Wetlands, 21: 155-159.

Joyeux J.C. & Ward A.B. 1998. Constraints on coastal

lagoon fisheries. Advances in Marine Biology,

34: 73-199.

Junk W.J. 2002. Long-term environmental trends and the

future of tropical wetlands. E n v i r o n m e n t a l

Conservation, 294: 414-435.

Junk W.J., Bayley P.B. & Sparks R.E. 1989. The flood

pulse concept in river-floodplain systems. In

D.P. Dodge ed. Proceedings of the internation -

al large rivers symposium. Can. J. Fish. Aquat.

Sci. Special Pub., 106: 110-127.

Junk W.J. & Wantzen K.M. 2003. The flood pulse con-

cept: New aspects, approaches and applica-

tions - an update. In R.L. Welcomme & T. Petr.

eds. Proceedings of the Second International

Symposium on the Management of Larg e

Rivers for Fisheries Volume 2. Phnom Penh,

Mekong River Commission.

River fisheries : Ecological basis for management and conservation 53

Kauffman J.B., Beschta R.L., Otting N. & Lytjen D.

1997. An ecological perspective of riparian

and stream restoration in the western United

States. Fisheries, 22: 12-24.

King A.J. 2002. Recruitment ecology of fish in floodplain

rivers of the southern Murray-Darling Basin,

Australia. Melbourne, Autstralia, Monash

University. (Doctoral dissertation)

King J.M., Brown C. & Sabet H. 2003. A scenario-based

holistic approach to environmental flow

assessments for rivers. River Research and

Applications, 19: (forthcoming)

King J.M., Cambray J.A. & Dean Impson N. 1998.

Linked effects of dam-released floods and

water temperature on spawning of the

Clanwilliam yellowfish Barbus capensis.

Hydrobiologia, 384: 245-265.

Koebel J.W. Jr., Harris S.C. & Arrington D.A. 1998.

Restoration of the Kissimmee River

Ecosystem in Central Florida, USA. In S.K.

Majumdar, E.W. Miller & F.J. Brenner, eds.

Ecology of Wetlands and Associated Systems.

Easton, Pennsylvania, Pennsylvania Academy

of Science. pp. 587-610.

Lae, R. 1997. Does overfishing lead to a decrease in

catches and yields? An example of two West

African coastal lagoons. Fisheries Manage-

ment and Ecology, 4: 149-164.

Large A.R.C. & Petts G.E. 1996. Rehabilitation of river

margins. In G. Petts & P. Calow, eds. River

restoration. Oxford, UK, Blackwell Science.

pp. 106-123.

Larinier M., Travade F. & Porcher J.P. 2002. Fishways:

Biological basis, design criteria and monitor-

ing. Bulletin Francais de la Peche et de la

Pisciculture, 364 Supplement. 208 pp.

Larsen T., Thilsted S.H., Kongsba K. & Hansen M. 2000.

Whole small fish as a rich calcium source.

British Journal of Nutrition, 83: 191-196.

Leung B., Lodge D.M., Finnoff D., Shogren J.F., Lewis

M.A. & Lamberti G.A. 2002. An ounce of

prevention or a pound of cure: Bioeconomic

risk analysis of invasive species. Proceedings

of the Royal Society of London, Series B -

Biological Sciences, 269: 2407-2413.

Lévêque C. 1995. Role and consequences of fish diversi-

ty in the functioning of African freshwater

ecosystems: A r e v i e w . Aquatic Living

Resources, 8: 59-78.

Lewis W.M., Hamilton S.K., Rodriguez M.A., Saunders

J.F. & Lasi M.A. 2001. Foodweb analysis of

the Orinoco floodplain based on production

estimates and stable isotope data. Journal of

the North American Benthological Society, 20:

241-254.

Livingston R.J. 1997. Trophic responses of estuarine fish-

es to long-term changes of river runoff .

Bulletin Marine Science, 60: 984-1004.

Lobon-Cervia J., Elvira B. & Rincon P.A. 1989.

Historical changes in the fish fauna of the

River Duero Basin. In G.A. Petts, H. Moller

and A.L. Roux, eds. Historical change of large

alluvial rivers: Western Europe. Chichester,

UK, John Wiley & Sons. pp. 221-232.

Loneragan N.R. & Bunn S.E. 1999. River flows and estu-

arine ecosystems: Implications for coastal fish-

eries from a review and a case study of the

Logan River, Southeast Queensland.

Australian Journal of Ecology, 244: 431-40.

Lorenzen K. 1996. The relationship between body weight

and natural mortality in fish: A comparison of

natural ecosystems and aquaculture. Journal of

Fish Biology, 49: 627-647.

54

Lorenzen K. 2000. Population dynamics and manage-

ment. I n M.C.M. Beveridge & B.J.

McAndreeds, eds. Tilapias: Biology and

exploitation. Dordrecht, Kluwer. pp. 163-225.

Lorenzen K. Aquaculture-based fisheries: Hatchery

organisms in fisheries management and con-

servation. Oxford, UK, Blackwell Publishing.

(forthcoming)

Lorenzen K. & Enberg K. 2002. Density-dependent

growth as a key mechanism in the regulation of

fish populations: evidence from among-popu-

lation comparisons. Proceedings of the Royal

Society of London, Series B - Biological

Sciences, 269, 49-54.

Lorenzen, K. & Garaway C.J. 1998. How predictable is

the outcome of stocking? In Inland Fisheries

Enhance men ts. FAO Fisheries Te c h n i c a l

Paper. 374. pp. Rome, FAO.

Lorenzen K., De Graaf G. & Halls, A.S. 2003. A biomass

dynamics model for assessing interactions

between fisheries and water management in

highly seasonal water bodies. L o n d o n ,

Imperial College.

Lorenzen K., Garaway C.J., Chamsingh B. & Warren T.J.

1998. Effects of access restrictions and stock-

ing on small water body fisheries in Lao PDR.

Journal of Fish Biology, 53 Supplement 1:

345-357.

Lorenzen K., Nguyen Khoa S., Garaway C.J., Arthur R.I.,

Chamsingh B., Litdamlong D., Siebert D. &

Innes-Taylor N. 2000. Impacts of irrigation

and aquaculture development on small-scale

aquatic resources. Final report to the DFID

Environment Research Programme. London,

Imperial College.

Session 3 Review :

Lorenzen K., Smith L., Nguyen Khoa S., Garaway C. &

Burton M. 2003b. Management of irrigation

development impacts on fisheries. Final

Report to the UK Department for International

Development. London, Imperial College.

Lowe-McConnell R.H. 1987. Ecological Studies in

Tropical Fish Communities. Cambridge,

Cambridge University Press. 382 pp.

McAllister D.E., Hamilton A.L. & Harvey B. 1997.

Global freshwater biodiversity: Striving for the

integrity of freshwater ecosystems. Sea Wind,

11: 1-140.

McAllister D.E., Parker B.J. & McKee P.M. 1985. Rare,

e n d a n g e r ed, and extinct fishes in Canada.

Syllogeus No. 54: 192 pp. Ottawa, Canada,

National Museums of Natural Sciences,

National Museums of Canada.

Malmqvist B. & Rundle S. 2002. Threats to the running

water ecosystems of the world. Environmental

Conservation, 29: 134-153.

Matsubara H. Sakai H. & Iwata A. 2001. A river metapop-

ulation structure of a Japanese freshwater

g o b y , Odontobutis obscura, deduced from

allozyme g en etic indices. E n v i r o n m e n t a l

Biology of Fishes, 61: 285-294

Mayden R.L. & Wood R.M. 1995. Systematics, species

concepts and the evolutionary significant unit

in biodiversity and conservation biology.

American Fisheries Society Symposium, 17:

58-113.

Meffe G.K. 1992. Techno-arrogance and halfway tech-

nologies: Salmon hatcheries on the Pacific

coast of North America. Conservation Biology,

6: 350-354.

Miller R.R., Williams J.D. & Williams J.E. 1989.

Extinction of North American fishes during the

past century. Fisheries, 146: 22-38.

River fisheries : Ecological basis for management and conservation 55

Minte-Vera C.V. 2003. Risk assessment of a floodplain

migratory fish subject to fisheries and dam-

operation procedures. Abstract submitted to

the Second International Symposium on the

Management of Large Rivers for Fisheries.

Phnom Penh, Mekong River Commission.

Mol J.H., Resida D., Ramlal J.S. & Becker C.R. 2000.

Effects of El Nino-related drought on freshwa-

ter and brackish-water fishes in Suriname,

South America. E n v i r onmental Biology of

Fishes, 59: 429-440.

Mosisch T.D. & Arthington A.H. 1998. A review of liter-

ature examining the effects of water-based,

powered recreational activities on lakes and

rivers. Lakes and Reservoirs: Research and

Management, 3: 1-17.

Moyle P.B. & Light T. 1996. Biological invasions of

freshwater: Empirical rules and assembly the-

ory. Biological Conservation, 78: 149-161.

Naiman R.J. & Decamps H. 1997. The ecology of inter-

faces: Riparian zones. Annual Review Ecology

& Systematics, 28: 621-658.

Naiman R.J., Bilb, R.E. & Bisson P.E. 2000. Riparian

ecology and the management of the Pacific

coastal rain forest. BioScience, 50: 996-1011.

Naiman R.J., Bunn S.E., Nilsson C., Petts G.E., Pinay G.

& Thompson L.C. 2002. Legitimizing fluvial

ecosystems as users of water. Environmental

Management, 30: 455-467.

Oberdorff T., Guegan J.F. & Hugueny, B. 1995. Global

patterns of fish species richness in rivers.

Ecography, 18: 345-352.

Oberdorff T., Hugueny B. & Guegan J.F. 1997. Is there an

influence of historical events on contemporary

fish species richness in rivers? Comparisons

between Western Europe and North America.

Journal of Biogeography, 24: 461-467.

Olden J.D. & Poff N.L. 2003. Redundancy and the choice

of hydrological indices for characterising

streamflow regimes. River Research and

Applications, 192: 101-121.

Parent S. & Schriml L.M. 1995. A model for the determi-

nation of fish species at risk - based upon life

history traits and ecological data. Canadian

Journal of Fisheries and Aquatic Sciences, 52:

1768-1981.

Pauly D., Christensen V. , Dalsgaard J., Froese R. &

Torres F. Jr. 1998. Fishing down marine food

webs. Science, 279: 860-863.

Peterson J.T. & Kwak T.J. 1989. Modeling the effects of

land use and climate change on riverine small-

mouth bass. Ecological Applications, 9: 1391-

1404.

Petersen R.C., Petersen L.B. & Lacoursiere J. 1992. A

building block model for stream restoration. In

P.J. Boon, P. Calow and G.E. Petts, eds. River

c o n s e r vation and management. C h i c h e s t e r ,

UK, John Wiley and Sons. pp. 293-309.

Petty J.T. & Grossman G.D. 1996. Patch selection by

mottled sculpin Pisces: Cottidae in a southern

Appalachian stream. Freshwater Biology, 35:

261-276.

Philippart J.C. 1995. Is captive breeding an effective

solution for the preservation of endemic

species? Biological Conservation, 72: 281-

295.

Poff N.L., Allan J.D., Bain M.B., Karr J.R., Prestegaard

K.L., Richter B.D., Sparks R.E. & Stromberg

J.C. 1997. The natural flow regime - a para-

digm for river conservation and restoration.

BioScience, 47: 769-784.

56

Poff N. LeRoy, Allan J.D., Palmer M.A., Hart D.D.,

Richter B.D., Arthington A.H., Rogers K.H.,

Meyer J.L. & Stanford J.A. 2003. River flows

and water wars: Emerging science for environ-

mental decision-making. Frontiers in Ecology

and the Environment, 16 due August 2003.

Polis G.A., Anderson W.B. & Holt R.D. 1997. Toward an

integration of landscape and food web ecolo-

gy: The dynamics of spatially subsidized food

webs. Annual Review of Ecology and

Systematics, 28: 289-316.

Post J.R., Parkinson E.A. & Johnston N.T. 1999. Density-

dependent processes in structured fish popula-

tions: Interaction strengths in whole-lake

experiments. Ecological Monographs, 6 9 :

155-175

Power M.E. 1992. Habitat heterogeneity and the func-

tional significance of fish in river food webs.

Ecology, 73: 1675-1688.

Puckridge J.T., Sheldon F., Walker K.F. & Boulton A.J.

1998. Flow variability and the ecology of large

rivers. Marine and Freshwater Research, 49:

55-72.

Pusey B.J. 1998. Methods addressing the flow require-

ments of fish. I n A.H.Arthington & J.M.

Zalucki, eds. Comparative evaluation of envi -

ronmental flow assessment techniques: Review

of methods. LWRRDC Occasional Paper

Series 27/98. Canberra, L an d and Wa t e r

Resources R & D Corporation. pp. 66-105.

Pusey B.J. & Arthington A.H. 2003. Importance of the

riparian zone to the conservation and manage-

ment of freshwater fishes: A review with spe-

cial emphasis on tropical Australia. Marine

and Freshwater Research, 54: 1-16.

Session 3 Review :

Pusey B.J., Arthington A.H. & Read M.G. 1995. Species

richness and spatial variation in assemblage

structure in two rivers of the wet tropics of

north Queensland. Environmental Biology of

Fishes, 42: 181-199.

Pusey B.J., Arthington A.H. & Read M.G. 1998.

Freshwater fishes of the Burdekin River,

Australia: Biogeography, history and spatial

variation in assemblage structure.

Environmental Biology of Fishes, 53: 303-318.

Pusey B.J., Burrows D. & Arthington A.H. 2003. The

translocation of recreationally desirable fishes

is detrimental to the maintenance of local bio-

diversity: Sleepy cod Oxyeleotris lineolatus

and other translocated species in the Burdekin

R i v e r , Australia. Abstract submitted to the

Second International Symposium on the

Management of Large Rivers for Fisheries.

Phnom Penh, Mekong River Commission.

Pusey B.J. & Kennard M.J. 1996. Species richness and

geographical variation in assemblage structure

of the freshwater fish fauna of the Wet Tropics

region of northeastern Queensland. Marine

and Freshwater Research, 47: 563-573.

Pusey B.J., Kennard M.J. & Arthington A.H. 2000.

Discharge variability and the development of

predictive models relating stream fish assem-

blage structure to habitat in north-eastern

Australia. Ecology of Freshwater Fishes, 9:

30-50.

Reeves G.H., Benda L.E., Burnett K.M., Bisson P.A. &

Sedell J.R. 1995. A disturbance-based ecosys-

tem approach to maintaining and restoring

freshwater habitats of evolutionarily signifi-

cant units of anadromous salmonids in the

Pacific northwest. American Fisheries Society

Symposium 17: 334-349

River fisheries : Ecological basis for management and conservation 57

Reckhow K.W. 1999. water quantity prediction and prob-

ability network models. Canadian Journal of

Fisheries and Aquatic Sciences, 56: 1150-1158

Reiser D.W., Ramey M.P. & Lambert T.R. 1989.

Considerations in assessing flushing flow

needs in regulated streams. In J.F. Craig and

J.B. Kemper, eds. Regulated rivers: Advances

in Ecology. New York, Plenum Press. pp. 45-

57.

Revenga C., Brunner J., Henninger N., Kassem K. &

Payne R. 2000. Pilot analysis of global ecosys -

tems: Freshwater systems. Washington, DC,

World Resources Institute. 83 pp.

Ricciardi A. & Rasmussen J.B. 1999. Extinction rates of

North American freshwater fauna.

Conservation Biology, 13: 1220-1222.

Richter B.D., Baumgartner J.V., Wigington R. & Braun

D.P. 1997. How much water does a river need?

Freshwater Biology, 37: 231-249.

Robinson C.T., Tockner K. & Ward J.V. 2002. The fauna

of dynamic riverine landscapes. Freshwater

Biology, 47: 661-677.

Rochet M.J. & Trenkel V.M. 2003. Which community

indicators can measure the impact of fishing?

A review and proposals. Canadian Journal of

Fisheries and Aquatic Sciences, 60: 86-99.

Roos N., Leth T., Jakobsen J. & Thilsted S.H. 2002. High

vitamin A content in some small indigenous

fish species in Bangladesh: Perspectives for

food-based strategies to reduce vitamin A defi-

ciency. International Journal of Food Sciences

and Nutrition, 53: 425-437.

Rose K.A., Cowan J.H., Winemiller K.O., Myers R.A. &

Hilborn R. 2001. Compensatory density

dependence in fish populations: Importance,

c o n t r o v e r s y , unde rstan ding an d prognosis.

Fish and Fisheries, 2: 293-327.

Saint-Paul U. 2003. Fisheries ecology of Amazonian

inundated forests. Paper presented to the

Second International Symposium on the

Management of Large Rivers for Fisheries

Schmutz S. & Jungwirth M. 1999. Fish as indicators of

large river connectivity: The Danube and its

tributaries. Archiv fur Hydrobiologie, 1999 3:

329-348.

Sedell J.R., Ritchie J.E. & Swanson F.J. 1989. The river

continuum concept: A basis for expected

ecosystem behaviour of very large rivers. In

D.P. Dodge ed. Proceedings of the internation -

al large rivers symposium, Can. J. Fish. Aquat.

Sci. Special Pub., 106: 49-55.

Shrestha T.K. 2003. Conservation and management of fishes in the large Himalayan rivers of Nepal. Paper presented to the Second International Symposium on the Management of Larg e Rivers for Fisheries.

So N. & Volckaert F.A.M. 2003. Preliminary results on

the genetic diversity and structure of the

migratory catfish. Pangasius bocourti in the

Cambodian Mekong River. Abstract submitted

to the Second International Symposium on the

Management of Large Rivers for Fisheries.

Phnom Penh, Mekong River Commission.

Sparks R.E. 1992. Risks of altering the hydrologic regime

of large rivers. In J. Cairns, B.R. Niederlehner

& D.R. Orvos, eds. Predicting ecosystem risk,

Vol XX. Princeton, USA, Princeton Scientific

Publ. Co. pp. 119-152.

Sparre P. & Willmann R. 1991. Software for bio-econom-

ic analysis of fisheries: BEAM4. FA O

Fisheries Technical Paper 310.

Stalnaker C., Lamb B.L., Henriksen J., Bovee K. &

Bartholow J. 1994. The instream incremental

methodology. A primer for IFIM. Biological

Report 29. Washington, DC, Department of the

Interior, National Biological Service.

58 Session 3 Review :

Stein B.A., Kutner L.S. & Adams J.S. eds. 2000. Precious

heritage: The status of biodiversity in the

United States. New York, Oxford University

Press. 416 pp.

Tharme R.E. 1996. Review of the international method-

ologies for the quantification of the instream

flow requirements of rivers. Report to the

South African Department of Water Affairs

and Forestry, Pretoria, South Africa, 116 pp.

Tharme R.E. 2003. A global perspective on environmen-

tal flow assessment: Emerging trends in the

development and application of environmental

flow methodologies for rivers. River Research

and Applications. 19. (forthcoming)

Thorpe J.H. & Delong M.D. 1994. The riverine produc-

tivity model: An heuristic view of carbon

sources and organic matter processing in large

river ecosystems. Oikos 70: 305-308.

Thorpe J.H., Delong M.D. Greenwood K.S. & Casper

A.F. 1998. Isotopic analysis of three food web

theories in constricted regions of a large river.

Oecologia, 117: 551-563.

Tockner K. & Stanford J.A. 2002. Riverine flood plains:

Present state and future trends. Environmental

Conservation, 293: 308-330.

Toth L.A., Obeysekera J.T.B., Perkins W.A. & Loftin

M.K. 1993. Flow regulation and restoration of

Florida’s Kissimmee River. Regulated Rivers:

Research and Management, 8: 155-166.

Toth L.A., Arrington D.A. & Begue G. 1997. Headwaters

restoration and reestablishment of natural flow

regimes: Kissimmee River of Florida. In J.E.

Williams, C.A. Wood & M.P. Dombeck, eds.

Watershed restoration: Principles and prac -

tices. Bethesda, Maryland, American Fisheries

Society. pp. 425-444

Toth L.A., Arrington D.A., Brady M.A. & Muszick D.A.

1995. Conceptual evaluation of factors poten-

tially affecting restoration of habitat structure

within the Channelized Kissimmee River

ecosystem. Restoration Ecology, 3: 160-180.

Toth L.A., Melvin S., Arrington D.A. & Chaimberlain J.

1998. Hydrologic Manipulations of the

Channelized Kissimmee River. Bioscience, 48:

757-764.

Trexler J. 1995. Restoration of the Kissimmee River: A

conceptual model of past and present fish com-

munities and its consequences for evaluating

restoration success. Restoration Ecology, 3:

195-210.

Valentin S., Souchon Y., and Wasson J.G. 1994.

Evaluation of hydro-peaking effects on fish

community and habitat. In I.G. Crowx ed.

Rehabilitation of freshwater fisheries. Oxford,

UK, Fishing News Books. pp. 138-151

Vannote R.L., Minshall G.W., Cummins K.W., Sedell J.R.

& Cushing C.E. 1980. The river continuum

concept. Canadian Journal of Fisehries and

Aquatic Sciences, 37: 130-137.

Va n Winkle W., Railsback S.F., Holcomb B.D. Studley

T.K., & Baldrige J.E. 1998. Individual-based

model of sympatric populations of brown and

rainbow trout for instream flow assessment:

Model description and calibration. Ecological

Modelling, 110: 175-207.

Walker K.F., Sheldon F. & Puckridge J.T. 1995. An eco-

logical perspective on dryland rivers.

Regulated Rivers: Research and Management,

11: 85-104.

Walters C.J. 1997. Challenges in adaptive management

of riparian and coastal ecosystems.

Conservation Ecology, 2: 1. (available at

http://www.consecol.org/vol1/iss2/art1)

River fisheries : Ecological basis for management and conservation 59

Ward J.V. 1989. The four-dimensional nature of lotic

ecosystems. Journal of the North American

Benthological Society, 8: 2-8.

Ward J.V. & Stanford J.A. 1983. The serial discontinuity

concept of lotic ecosystems. In T.D. Fontaine

& S.M. Barkeu, eds. Dynamics of lotic ecosys -

tems. Ann Arbor, USA, Science. pp. 29-42.

Ward J.V. & Stanford J.A. 1995. Ecological connectivity

in alluvial river ecosystems and its disruption

by flow regulation. Regulated Rivers:

Research and Management, 11: 105-119.

Ward J.V., K. Tockner & F. Schiemer 1999. Biodiversity

of floodplain ecosystems: Ecotones and con-

n e c t i v i t y . Regulated Rivers: Research and

Management, 15, 125-139.

Ward J.V., Tockner U., Uehlinger U. & Malard F. 2001.

Understanding natural patterns and processes

in river corridors as the basis for effective river

restoration. Regulated Rivers: Research and

Management, 117: 311-323.

Warren T.J., Chapman G.C. & Singhanouvong D. 1998.

The upstream dry-season migrations of some

important fish species in the Lower Mekong

River of Lao PDR. Asian Fisheries Science,

11: 239-251

World Commission on Dams 2000. Dams and develop-

ment: A new framework for decision making.

The Report of the World Commission on

Dams. London, Earthscan Publications, 448

pp.

Welcomme R.L. 1979. Fisheries Ecology of Floodplain

Rivers. London, Longman. 377 pp.

Welcomme R.L. 1985. River Fisheries. FA O Fish. Tech.

Pap. No. 262. Rome, FAO. 330 pp.

Welcomme R.L. 1988. International introductions of

inland aquatic species. FAO Fisheries

Technical Paper 294. 318 pp.

Welcomme R.L. 1999. Review of a model for qualitative

evaluation of exploitation levels in multi-

species fisheries. Fisheries Management and

Ecology, 6: 1-20.

Welcomme R.L. 2001. Inland fisheries ecology and man-

agement. Oxford, UK, Blackwell Science

Ltd., Fishing News Books. 358 pp.

Welcomme, R.L. & Bartley, D.M. 1998. Current

approaches to the enhancement of fisheries.

Fisheries Management and Ecology, 5: 351-

382.

Welcomme R.L. & Hagborg D. 1977. Towards a model of a floodplain fish population and its fishery. Environmental Biology of Fishes, 21: 7-24

Welcomme R. & Halls A. 2003. Dependence of river fish-eries on river flow. In Welcomme R.L. & Petr T. eds. P r oceedings of the Second

International Symposium on the Management

of Large Rivers for Fisheries Volume 2. Phnom Penh, Mekong River Commission.

Williamson M.H. & Fitter A. 1996. The characters of suc-

cessful invaders. Biological Conservation, 78:

163-170.

Winemiller K.O. 1989a. Ontogenetic diet shifts and

resource partitioning among piscivorous fishes

in the Venezuelan llanos. E n v i r o n m e n t a l

Biology of Fishes, 26: 177-199.

Winemiller, K.O. 1989b. Patterns of variation in life his-

tory among South American fishes in seasonal

environments. Oecologia, 81: 225-241.

Winemiller, K.O. 1996. Dynamic diversity: Fish commu-

nities of tropical rivers. In M.L. Cody & J.A.

Smallwood, eds. Long-term studies of verte -

brate communities. Orlando, Academic Press.

pp. 99-134.

60

Winemiller K.O. 2003. Floodplain river food webs:

Generalizations and implications for fisheries

management. In R.L. Welcomme & T. Petr,

eds. Proceedings of the Second International

Symposium on the Management of Larg e

Rivers for Fisheries Volume 2. Phnom Penh,

Mekong River Commission.

Winemiller K.O. & Jepsen D.B. 2002. Migratory

neotropical fish subsidize food webs of olig-

otrophic blackwater rivers. In G.A. Polis, M.E.

Power & G. Huxel, eds. Food webs at the

landscape level. Chicago, University of

Chicago Press. (forthcoming)

Winemiller, K.O. & Rose, K.A. 1992. Patterns of life-his-

tory diversification in North American fishes:

Implications for population regulation.

Canadian Journal of Fisheries and Aquatic

Sciences, 49: 2196-2218.

Wissmar R.C. & Beschta R.L. 1998. Restoration and

management of riparian ecosystems: A catch-

ment perspective. F r eshwater Biology, 4 0 :

571-585.

Woodward G. & Hildrew A.G. 2002. Food web structure

in riverine landscapes. Freshwater Biology, 47:

451-468.

Zalewski M. 2003. Ecohydrology - new conceptual tool

for restoration and sustainable use of fisheries

resources in rivers. Abstract submitted to the

Second International Symposium on the

Management of Large Rivers for Fisheries.

Phnom Penh, Mekong River Commission.

Zhong Y. & Power, G. 1996. Environmental impacts of

hydroelectric projects on fish resources in

China. Regulated Rivers: Research and

Management, 12: 81-98.